Click here for our Site Map

English Writing Services

scientific, thesis, technical
and business editing service

Glossary of Geology Terms

ABANDONED Forsaken by its owner or holder. To give up or discontinue any interest in. A word used in reference to a mine or a person's claim, right, or interest in the undiscovered minerals in an area of land.

Abrasion A type of mechanical weathering to which loose fragments or pieces of rocks and minerals are subjected during transport by water or air as they collide with, and scrape against, each other and stationary rocks.

Absolute Age See Radiometric Age.

Accessory Mineral Any mineral that occurs with another mineral, but does not appear in its name. An accessory mineral is incidental to the dominant mineral(s) in a particular rock. Examples of accessory minerals include corundum, monazite, allanite, tournaline, muscovite, pyroxene, and olivine.

Acclivity An upward slope of a hill. An ascending slope. See also Declivity, Steep

Accretion The adding on to property. The term most frequently denotes the gradual and imperceptible growth or increase in land due to natural causes as may occur along the seashore or a river by the deposition of sand or silt. Accretion refers also to the acquisition of title to this additional land. Title belongs to the owner of land to which this increase or growth attaches. Accretion of land may occur by alluvion (the deposit of alluvium) or by dereliction, as when a body of water, such as a sea, recedes. Such land exposed by the gradual receding of water is known as a reliction.

Accretion Bar: A low-level deposit of sand and gravel formed in a stream by the gradual addition of new material. Accretion bars are typically formed along the short or inside radius of curves.

Acid In the study of minerals and rocks, silica is called an acid. The term applies also to any siliceous material that is mainly composed of silica (silicon dioxide).

Acre A commonly used unit of land area. It is equal in area to 43,560 square feet or, alternatively, 4,840 square yards, 160 square rods, 10 square chains, 10,000 square links, or 0.405 hectares. An acre is an area equal to a tract of land measuring 208.71 feet by 208.71 feet. The acre originated as the amount of land which a yoke of oxen could plow in one day. A section is comprised of 640 acres.

Actinolite A variety of amphibole, occurring in bright greenish crystals or in masses. It is similar in composition to tremolite, but contains iron. Actinolite is a non-hazardous relative of asbestos and has fibers that are fine and silky and have appreciable tensile strength. In addition to iron, it contains silica, calcium, and magnesium. Actinolite is a common mineral in metamorphic rocks.

Active Volcano A volcano that is erupting or about to erupt. Also, one that has erupted within recent history and, it is believed, will probably to do so again in the near future.

Adit A nearly horizontal passage driven leading into a mine. An opening into the side of a mountain or hill to access a mineral deposit. The term, tunnel, is frequently used instead of adit. However, a tunnel normally opens on both ends to the surface.

Aeolian Soil Soil consisting of materials which have been deposited by the wind. See also Soil

Agglomerate A breccia consisting mainly of rocks of volcanic origin. Although similar in appearance to a conglomerate, an agglomerate is composed of volcanic bombs, which were ejected in a liquid or plastic state.

Alabaster A massive, fine-grained variety of gypsum that is snow-white and translucent. It has been used for centuries for statutary and other ornaments. Also called Oriental Alabaster.

Alkaline Flat An arid plain, which formerly was the bed of a saline lake, having soil encrusted or impregnated with alkaline salts. The term, alkaline flat, is typically applied only to flats in the western United States. A well-known example is the Bonneville Salt Flats west of Salt Lake City. An alkaline flat is also known as a salina or salt flat. See also Soil, Desert

Alluvial Of, or pertaining to alluvium, a deposit of sand or mud formed from flowing water, or to processes associated with the transportation and deposition by running water. The word is used in reference to minerals that are associated with deposits made by flowing water.

Alluvial Fan A fan-shaped alluvial deposit left by a stream where its bed becomes less steep, such as where a stream issues from a gorge to enter an open plain. An alluvial fan often forms where a stream issues from mountains onto a lowland. See Alluvium

Alluvial Gold Gold that has been discovered in association with water-worn material.

Alluvial Plain See Flood Plain

Alluvial Placer Loose gravel of any size, soil, or mud that has been transported and deposited by flowing waters, such as streams or creeks, and depositing placer gold and other valuable minerals. An alluvial placer is also known as an alluvial deposit.

Alluvium The increase in land due to the gradual and unapparent action of natural forces, such as may be effected by the transport and depositing of silt by flowing water. Alluvium applies primarily to deposits formed in floodplains and deltas. However, the term also applies to any point at which a river overflows its banks or is slowed. This last instance occurs where the river enters a lake or other large body of water. Accretion refers to the act by which alluvium is created. In contrast to accretion, avulsion is sudden and discernible. Alluvium is also called alluvion. See also Accretion, Avulsion, Diluvial

Alteration A chemical change in minerals occurring after they are formed; such as the reaction between hydrothermalizing solutions and rock, and also the surface weathering of rock. For example, feldspars may have altered to clay. A mineral, such as hornblende, may be altered to chlorite.

Amalgam An alloy of mercury with another metal, such as gold or copper. Also, a mixture.

Amalgamated Gold Gold found during a placer mining operation that has traces of mercury on it. Amalgamated gold is also called mercury gold.

Amber A fossil resin, usually of a yellow color, but sometimes reddish, brownish, or whitish. When heated, amber softens and melts. It occurs as irregular nodules, rods, or drop-like shapes.

Amorphous Without a definite crystal structure or form, as illustrated by obsidian. Also, occurring in a mass without stratification.

Amphibole Any of a complex group of hydrous silicate minerals that form needlelike crystals and contain calcium, magnesium, sodium, iron, and aluminum. The group includes hornblende, actinolite, tremolite, asbestos, etc. It occurs in many igneous and metamorphic rocks.

Amphibolite A metamorphic rock that consists primarily of an amphibole, usually hornblende.

Andesite A dark, fine-grained igneous volcanic rock of the composition of diorite. It has more silica than does basalt, but less mafic than basalt. It typically has visible crystals of plagioclase feldspar. Andesite usually occurs as a surface deposit and in lava flows.

Angle of Dip The angle of inclination from the horizontal plane of strata or mineral deposits.

Anomaly A geological feature, which is a different than its surroundings and may be an indicator of the presence of mineralization.

Anthracite A very hard, black, glassy coal that has an almost metallic luster. Anthracite has a carbon content of 92% to 98% and the lowest amount of volatile matter. This gives it a higher heat or calorific value than other forms of coal. Anthracite .It burns with a hot, pale blue flame and very little smoke, but is difficult to ignite. Anthracite is develops from lignite and bituminous coal through metamorphism. It is the most highly metamorphosed form of coal and the least plentiful. Less than one percent of all coal discovered in North is anthracite

Anticline An upward-curving (convex) fold in rock strata. The middle part contains the oldest section of rock. It appears below the surface in the form of an elongated dome. Anticlines are good prospects for drilling because any oil in the strata will rise to the highest point of the formation because the specific gravity of oil is less than that of water. An anticline is the opposite of a syncline. See Syncline.

Aphanitic Texture A term that is applicable to igneous rocks in which the constituent minerals cannot be detected with the naked eye.

Aplite A granite of very even, fine-grained texture that occurs in narrow dikes cutting through larger granite masses. It is higher in silica than the main mass of granite.

Aquifer An underground geological formation of water-bearing porous rock, sand, or gravel, which is saturated with water and which it releases in significant amounts for wells and springs. An aquifer is also called a water-bearing stratum, lens, or zone. See also Water Table

Argillaceous Clayey. Of the nature of, or resembling, clay.

Argillite Any compact sedimentary rock, composed primarily of clay materials. Clay stone. Argillite includes shale, mudstone, and siltstone.

Arkose A variety of sandstone that is rich in feldspar and quartz, It is a sandstone derived from granite or gneiss

Arroyo A dry gully or channel carved by water and lying in a semiarid or arid desert area, which is subject to flash flooding. The bed of an intermittent stream. Also, termed wash, dry wash, or coulee. In Spanish, arroyo is a stream, brook, or watercourse whereas an arroyada is a gully or flood. See Coulee.

Artesian Well A perpendicular hole or boring into the ground from which water is forced in a continuous flow because of internal pressures on the water-bearing stratum below.

Rainfall percolating through the soil into aquifers (underlying rocks, such as limestone, sandstone, and basalt, through which water can migrate) may become confined between two impermeable rock layers. Should these layers be tilted or folded to form a trap, the water contained in the lower part of the aquifer may be subject to pressure. If this pressure is sufficiently great and a well is sunk through the strata overlaying the permeable rock, water will be forced through the opening to the surface. See also Aquifer, Groundwater.

Assay To test a material (e.g., metal or oil) for quality, fineness, or purity, or to determine the constituents of an alloy. Also, the chemical analysis of samples of precious metals or other minerals. Chemicals are used in a wet assay. Chemicals and fire are used in a fire assay. Gold and silver are usually assayed by fire.

Atoll A ring-shaped coral island or reef, which nearly (or completely) encircles a lagoon. The ribbons of reef comprising an atoll may not always be circular. However, the general shape of an atoll is closed. It may be several miles in diameter and enclose a lagoon having a maximum depth well in excess of one hundred feet. The reef may be cut by channels providing entry to boats.

Avulsion The sudden removal of soil or land from a tract by a flood. Also, a similar loss of land in an owner's property because of a sudden change in the course of a river or stream, which separates two properties. In the second case, land may be severed from the tract of one owner and added to that of another. Avulsion differs from accretion in the immediacy and discernible nature of the change. When the change is abrupt, the boundary separating the properties remains unchanged.

Badlands Arid, barren desert lands, which are characterized by severe erosion of the soft surface strata. The erosion produces many ridges, peaks and gullies, and other strange forms. Such lands may be found in certain areas of the western part of the country, including South Dakota. See also Desert.

Bar A raised body of sand or alluvium, which has been deposited on the bed of a stream, lake, or sea. Often, a bar may be found at the entrance to a river. See also Sandbar

Barranca A Spanish word denoting a deep rock-walled ravine, gorge, or canyon having precipitous sides. See also Canyon, Gorge, Ravine

Barrel The standard unit of volume measurement for crude oil and various petroleum products. One barrel is equal in volume to 42 U.S. gallons, 158.89 liters, 9,702 cubic inches, 5.6146 cubic feet, 34.9722 Imperial gallons, or 0.15899 cubic meters. The Petroleum Producers Association adopted the 42-gallon barrel in 1872. This quantity was a volume of 40 gallons plus an additional allowance of two gallons on each barrel in favor of the buyer.

Barren Rock Rock or vein material that contain no minerals in quantities sufficient to permit them to be mined profitably.

Basalt The dense, fine-grained, mafic igneous rock of a lava flow or minor intrusion. It has a silica content of 40% to 55% and is usually rich in iron, calcium, and manganese. It is gray-black to black in color. Basalt is the most abundant volcanic rock in the Earth's crust.

Basement: Rock Basement rock is the oldest rock recognized in a particular. It underlies any sedimentary rocks and is a combination of igneous and metamorphic rocks. The typical basement rock was formed during the Precambrian or Paleozoic in age.

Base Metal A term applicable to the main industrial non-ferrous metals, excluding precious metals and minor metals. Metals that are not noble or precious, but serve as a base for objects covered with precious metals. They are copper, aluminum, lead, nickel, tin, and zinc. Base metals are traded on the London Metals Exchange. In addition, copper is traded on the New York Mercantile Exchange.

Basin A hollow or depression of extensive area in the Earth's surface, such as a valley, which has no surface outlet and into which adjacent land drains. Also, the entire region drained by a river and its tributaries. In addition, the word, basin, serves to denote a partially enclosed, sheltered area along a shore, river, or canal, in which boats or ships may be moored or docked. Finally, a basin may be any natural or artificial hollow, enclosed spot containing water, whether an inlet or pond or merely a cistern.

Batholith A very large, irregular body of intrusive, igneous rock, bounded by irregular, crosscutting surfaces or fault planes. It is believed to have crystallized at a considerable depth below the earth's surface. Batholiths are usually found in mountain ranges after the country rock, which covered them, has eroded.

Bauxite A rock consisting of hydrous aluminum oxide or hydroxide with various impurities. Bauxites are formed by the weathering of many different rocks various and vary with the origin and geologic history of their deposits. Some bauxite deposits are hard and dense, whereas others are soft and easily crushed. Bauxite may grade into laterite or clay. It is the principal aluminum ore.

Bayou A marshy area caused by the overflowing of a lake or river. Also, an intermittent stream formed in an abandoned channel of a river. See also Marsh.

BBL An abbreviation for barrel. Less frequently used is BL. See Barrel.

BCF Billion cubic feet. The volume of natural gas is measured in cubic feet. See also Natural Gas

B/D Barrels per day. A term used to describe the output of an oilfield or capacity of a refinery. See also Barrel, Crude Oil

Beach That sloping shore of a body of water, which is situated between high and low water marks. In particular, an expanse of sand or pebbles along a seashore. A term synonymous with shore or strand. See Shore, Strand, Tide.

BedA layer or stratum of sediment, sedimentary rock, coal, or other sedimentary deposit.

Bedding The various parallel layers in sedimentary rock (beds) that are differentiated from each other by chemical composition, grain size, and other subtle differences.

Bed Load The cobblestone, rocks, coarse particles, and other debris that slide, bounce, and roll along the bottom of the channel of a stream, particularly in flood waters. The term is also spelled bed lode Grounding is the term that applies when these larger pieces cease their movement as flooding recedes.

Bedrock The layer of rock below the surface soil and vegetation of land. In some rocky areas, bedrock may lie exposed at the surface. See Soil Mantle.

Bench A strip of level, elevated land between a river and neighboring hills or along a coast. Also, any elevated expanse of earth or stone, which has a flat surface.

Beneficiation The treatment of ore for smelting. The treatment of mined material to make it concentrated or richer prior to smelting.

Bentonite A clay material consisting mainly of the mineral montmorillonite. It has the ability to absorb large quantities of water and expand its normal volume by to several times. It is used for a number of purposes, including decolorizing petroleum products.

Biostratigraphy The study of rock strata, including their distribution, age, and environment of deposition, based on their fossil content.

Biotite A very common mineral in the mica family. Biotite occurs in black, dark brown, or green sheets that peel apart. It is a silicate that is rich in iron, magnesium, potassium, and aluminum, and is a key constituent of igneous rocks. Biotite is often mistaken for fool's gold.

Bit The boring head used at the end of a drill rod that is used to dig a circular hole in rock or drill oil wells. Often detachable, it consists of a horizontally rotating blade or an assembly of rotating toothed wheels. The size of the bit determines the size of the hole.

Bitumen Any of various solid and semi-solid substance that consist primarily of hydrocarbons and which can be converted into liquid form by heating. Bitumens can be refined to produce commercial products, such as gasoline, fuel oil, and asphalt.

Bituminous Coal A shiny black, mineral coal that contains volatile hydrocarbons and tarry matter, and burns with a yellow, smoky flame. A coal that is between sub-bituminous and anthracite coal. It develops from deeply buried lignite as a result of heat and pressure. Bituminous coal has an 80% to 93% carbon content. It typically has a high BTU value and is a more efficient heating fuel than lignite. Bituminous coal is the most common grade of coal. See also Anthracite, Lignite.

Bluff A cliff or a high, steep bank having a broad precipitous face.

Blowouts An uncontrolled releases of gases, fluids, or solids, as from a newly drilled gas or oil well.

Bog A wetland identifiable by sphagnum mosses and heaths. In contrast to bogs, swamps are dominated by trees and marshes by grasses. Bogs are found in moist, depressed land formed by the retreat of glaciers and having poor drainage. Precipitation provides their only source of water. (Bogs fed by springs or other waters are known as fens.) The low oxygen level in a bog retards plant decay. Dead vegetation, which settles to the bottom, becomes peat, a forerunner of coal. Although swamps and some marshes produce peat, the accumulation of peat is greatest in bogs. There, sphagnum mosses excrete antibiotics and raise the water acidity. See also Marsh, Peat Bog, Sink, Swamp, Wetlands.

Borehole Any deep or long drill-hole, drilled into the ground, using a drilling rig and a diamond drill. The uncased drill hole is just large enough to install a well casing and extends from the surface to the bottom of the well

Bottom Land Low-lying land, particularly level ground, near an often flooded river, lake or stream. Also, lowland situated in a valley or dale or land, such as tideland or a flood plain, which is often under water. See also Flood Plain, Highland.

Box Canyon A narrow canyon, which has nearly vertical walls of rock and a relatively flat bottom.

Breccia Rock composed of broken, angular particles that commonly are cemented together. It is often not sedimentary as the broken material has been consolidated without transportation and wearing by water.

British Thermal Unit (BTU) One British Thermal Unit is the amount of energy required to raise the temperature of one pound of water (slightly more than one pint) by one degree (from 58.5 to 59.5 degrees) on the Fahrenheit scale under standard pressure of 30 inches of mercury. One Btu equals 252 calories, (gram), 778 foot-pounds 1,055 joules or 0.293-watt hours. The BTU is commonly used as a measure of the heat energy of different fuels. Prices of various fuels involving differing units of volume measure can be more easily compared when expressed in dollars and cents per million BTUs.

Brow The projecting edge of a cliff or hill. Also, that point at which a gentle slope becomes more abrupt. The word, brow, is also used also in reference to the projecting edge of a pillar, wall, etc. A ledge or verge. See Verge.

Bulk Sample A sample of mineralized rock in excess of fifty tons. It is collected as a sample that is representative of a potential body of ore It is used to determine metallurgical characteristics.

Bullion Bars, wafers, or ingots of refined gold or silver. Popular use of the word has been broadened to include platinum, palladium, and other precious metals. See also Fineness, Fine Weight, Gold, Gold/Silver Ratio, Precious Metals, Silver.

Butte An isolated hill or peak, which rises abruptly. The summit may be flat, rounded, or pointed. The sides are steep and precipitous. A butte is formed by the erosion of the surrounding flat, lying strata. The width of a butte is less than its height. See Mesa.

By-Product Any mineral, or mineral product, from a mine or refinery operation that is additional and secondary to the primary mineral sought.

Calcareous An adjective that describes a rock or other earth material that contains an abundance of calcium carbonate (CaCO3). For example, a calcareous sandstone has a calcium carbonate content of up to 50%.

Calcite One of the most common minerals, calcite consists of calcium carbonate (CaCO3). It generally is white in color and can be easily scratched with a knife. Calcite is polymorphous (same chemical, but with different crystal structures) and appears in a variety of different crystalline forms. Calcite is the most important mineral in limestone and marble.

Caldera The large, circular depression in the top of a volcanic cone, caused by the inward collapse of the cone as the magma below the volcano subsides. Volcanic ash, falling back to earth, fills the caldera. A caldera is at least a mile in diameter. See also crater.

Caliche A surface deposit that consists of sand or clay impregnated with crystalline salts, such as sodium chloride or sodium nitrate.

Canyon A deep gorge or ravine having steep, cliff-like walls rising from the bed of a stream, which flows through it. Also, spelled kanyon. It derives from the Spanish word cañon.

Carat A unit of measurement to express the weight of diamonds and certain other precious gems, including ruby, sapphire, emerald, topaz, aquamarine, garnet, tourmaline, zircon, spinel, and occasionally pearl and opal. One carat is equal to 0.200 grams. A point is equal to 1/100th of one carat (or 2 milligrams). See also Karat.

Carbonaceous Of, like, or containing carbon. Rich in carbon or organic matter.

Carbon-14 (C) A radioactive isotope of carbon that has six protons and eight neutrons in its nucleus, rather than the six protons and six neutrons of carbon-12, the stable isotope that accounts for almost 99% pf carbon found in nature. High-energy neutrons, produced by cosmic ray interaction in the upper atmosphere, react with N-14 to form C-14. In turn, C-14 mixes with carbon in the lower atmosphere, making C-14 available naturally. C-14. has a half-life of 5,730 ears.

Carbon-14 Dating An isotope dating technique that is based on the rate of decay of carbon-14 to nitrogen-14. The 5,730-year half-life of carbon-14 facilitates the estimation of the ages of rocks containing carbon-14 that are between 100 and 100,000 years old. See also Potassium-Argon Dating.

Carbonate Any of several minerals that contain one central carbon atom with strong covalent bonds to three oxygen atoms and ionic bonds to one or more positive ions. Also, a sedimentary rock composed mainly of calcium (Ca) or Magnesium (Mg) and carbonate (CO3) ions. Limestone and dolomite are examples of common carbonate sedimentary rocks.

Carbonic Acid A weak acid formed when carbon dioxide dissolves in water. This acid plays a role in the creation of stalactites and stalagmites.

Cascade A water fall or a series of small falls formed by a rocky descent in the bed of a stream. Also, artificially created falls of this nature in landscape gardening.

Casing The nine-meter, steel tubes that are connected by threaded sleeves ad used to line the inner wall of a drill hole. Cement is injected into the space between the casing and the hole wall.

Casinghead Gas Unprocessed natural gas which is present in an oil well and removed as it flows up the well's casing to the surface. It contains natural gasoline and other liquid hydrocarbon vapors. Natural gas is bought and sold as a commodity on the New York Mercantile Exchange.

Cataract A waterfall of considerable size and in which the water flows over a precipice in one sheer drop. It is distinguished from a cascade by a much greater volume of water.

Catch A fixed location, such as a crack, crevice, hole, fault, outcropping, or other obstruction where gold has been caught or trapped, despite the movement of the flowing water. Catch is short for gold catch.

Cave A hollow, and more or less horizontal, naturally formed space below ground. A natural opening in the earth that is large enough for a human to enter and that extends beyond the reach of sunlight. A cavern in the earth. Also, a chamber in a mountainside.

Cavern A large, natural underground or underwater chamber or series of chambers. A large or extensive cave.

Cay A small, low island of sand or coral. Also, a reef or a low, islet-like bank of sand, rock, coral, etc.

CF/D Cubic feet per day. A unit of volume measurement used in reference to the movement of natural gas through a pipeline.

Chalcocite An important copper mineral ore that is fine-grained, brittle, leaden gray to black in color with a metallic luster. It has a tendency to tarnish to bluish or greenish colors on fresh surfaces. Chalcocite resembles argentite in color and general appearance.

Chalcopyrite A copper and iron sulfide, chalcopyrite is the most common mineral of copper and an important ore. It is often mistaken for fool's gold. The mineral tarnishes easily, turning from brassy yellow or bronze to yellowish or grayish brown. It is typically found in ore veins. Chalcopyrite, copper sulfide, is a sulfide mineral that crystallizes in the tetragonal system and has a crystalline structure related to sphalerite.

Chalk A soft, friable, white to grayish sedimentary rock formed from the remains of tiny seashells and high in calcium carbonate (CaCO3). It contains varying amounts of silica, quartz, feldspar, or other mineral impurities. It is used as a mild abrasive in toothpaste, as a filler, extender, or pigment in ceramics, putty, cosmetics, crayons, paper, and other products, for drawing, and in many other applications.

Channel Sample A sample consisting of pieces taken from a small channel or trench cut across a vein or mineral deposit or rock exposure. The channel is usually about 4 inches wide and 1 inch deep.

Chemical Sediment Sediment that was formed at or near its place of deposition by chemical precipitation, usually from seawater. It consists of minerals that were previously in solution, but which were precipitated from water that has since evaporated or become oversaturated.

Chemical Weathering The total of all chemical reactions that act on rock and minerals exposed to water and atmosphere and alters their chemical compositions to more stable forms by removing and/or adding elements. See also Mechanical Weathering.

Chert A dense, very hard, sedimentary rock consisting of amorphous or extremely fine-grained quartz, with minor impurities and partially hydrous. Chert may be either organic or inorganic, although the inorganic forms are most common. Chert is brown in color. There are several varieties of chert: jasper, chalcedony, agate, flint, opal, and novaculite. Black chert is called flint.

Chlorite A group of minerals, hydrous silicates of aluminum, ferrous iron, and magnesium, that occur in green plate-like crystals or scales. They resemble mica in the shape of the crystals. However, the chlorite scales are not elastic. Chlorites form as the result of alteration of micas in the presence of moisture.

Chondrule A small nugget of rocky material, such as olivine or pyroxene, that is found in stony meteorites. It is believed that this matter was formed about five billion years ago.

Christmas tree An oil industry term for a wellhead. The arrangement of pipes, nozzles, control valves, gauges, and thermometers, etc., at the exit from a production well.

Cinder cone A volcanic cone formed entirely of loose pyroclastics expelled from the vent by escaping gases.

Cirque A circular valley, plain, or space encircled by steep walls or heights high in the mountains and caused by glacial erosion. A natural amphitheater.

Claim A piece of public land for which a formal request is made for mining or other purposes. A right that grants its holder the exclusive right to search for minerals within a specified area of land. A prospector or mining company will mark its claimed area by the use of stakes.

Claim Jumper One who appropriates a mining claim already taken by another. See also Claim, Mineral Rights.

Clastic Rock A sedimentary rock that has been formed from the particles or fragments of previously existing rock, which were mechanically transported from their place of origin (e.g., sandstone, shale).

Clay A natural earthy mineral which is plastic when wet, consisting largely of hydrated silicates of aluminum. They are generally formed by the chemical weathering of silicate-bearing rocks.

Claystone Sedimentary rock consisting of clay. Argillite.

Cleavage The cleaving or splitting of a crystal, mineral, or rock, etc., along distinct planes, so as to yield smooth surfaces. Also, the tendency of a mineral to break along crystallographic planes.

Cliff A high and perpendicular or steep face of rock. Cliffs are often found on the seashore or overhanging a lake or river.

Coal A carbonaceous, sedimentary rock that is solid, brittle, combustible, and black or brownish-black in color. Coal is formed from partially or completely decomposed plant remains. Carbon makes up more than 50 percent of its mass. Coal is widely used as a fuel

Coal mine A mine or pit from which coal is mined. The term usually includes the land and all structures, excavations, machinery, and other property that is associated with the extraction of coal from its natural deposits.

Coastal plain A plain of little relief that extends along a coast.

Cobblestone A naturally rounded stone that is suitable for use in paving.

Col A depression between two mountains. A gap in a ridge, which provides a pass between valleys. A saddle.

Color A term used in reference to any small grains or flakes of gold left in a prospector's pan after a sample of earth or concentrate has been washed. Also termed a shiner.

Commercial Silver A tradable form of silver that has a fineness of 99.9 per cent or greater. Commercial silver is usually sold in bars of 1,000 oz. each. See also Fineness, Silver.

Compaction The consolidation of sediments due to the weight of overlying deposits. The process by which the volume or thickness of sediment is reduced due to pressure from above. Along with cementation, this converts sediments to solid rock.

Complex Ore An ore named for two or more valuable metals (e.g., lead-zinc ore), one or more of which are of economic value.

Compound Any chemical combination of two or more elements that have been combined in specific and constant proportions. The physical characteristics of a compound differ from those of its constituent elements. Water (hydrogen and oxygen) and carbon dioxide (carbon and oxygen) are two examples of (chemical) compounds.

Concentrate An enriched fraction of an ore after most of the waste rock has been removed. The concentrate contains the valuable metals and forms the raw material for smelting.

Concretion A rounded mass of mineral matter, such as silica or calcite, that occurs in sandstone, clay, etc., often in concentric layers about a nucleus, such as a leaf, shell, or fossil.

Conglomerate A rock that consists of rounded and water-worn pebbles or the like that are embedded in a finer cementing material. Consolidated gravel. Conglomerates contrast with breccias, which consist of angular fragments.

Continental shelf That part of a continent's landmass that is covered by the sea or ocean. The continental shelf extends outward at a very gentle slope to a depth of, typically, 200 meters.

Contour A contour is a line, which traces points of equal altitude (elevation). The distance between contours varies inversely with the slope of the land. One may liken contours to lines, such as would be traced by successive shorelines of an imaginary sea rising over the land.

It is a common practice in mapping to show contours of equal intervals of height above sea level. Every contour closes upon itself either within or outside the limits of the map. A contour line closing within the limits of the map denotes either a summit or a depression. Alternatively, the term, contour, refers to the portrayal on a map of the intersection of the surface of the ground by a level surface. See Contour Interval, Contour Map, Topographic Map

Contour Interval The vertical distance (difference in elevation) that is represented by any two consecutive contour lines on a map that uses contour lines to represent elevation. See Contour Map, Topographic Map.

Contour Map A map providing the various elevations of the land or site, which it illustrates, by means of contour lines. These are lines of equal elevation. A topographical map usually is a contour map. It shows the relief of an area by using contour lines to represent different and specific elevations. Each contour passes through points of equal elevation. Geophysical, geochemical, and other variables also are illustrated by contour maps. See also Contour, Topographic Map

Conventional Mining The fully mechanized approach to underground mining that involves the insertion of explosives into a seam or the ore body, the detonation of the explosives, and the removal of the ore by a loading machine to a conveyor or shuttle car.

Core The innermost part of the Earth, consisting mostly of iron and nickel. The core lies beneath the mantle and is the densest part of the Earth. It is believed that the core has an inner part, which is liquid, and an outer part, which is solid. The term, core, also is used in reference to a core sample. See also Core Sample, Crust, Mantle.

Core Sample The long cylindrical piece of rock, about one inch or more in diameter, that is recovered by diamond drilling during exploration. An analysis of the core sample provides information of the geology and chemistry of the various strata. (

Coulee A deep ravine or gulch cut, which is created by heavy rain or melting snow, but is usually dry during the summer. A term, which is sometimes used to denote a Wash or Arroyo.

Country Rock The rock surrounding and intruded by igneous intrusions or mineral veins. Country rock is also called wall rock.

Cove A small bay, creek, inlet, or other recess in a coast where boats may shelter.

Cover Another term for overburden. See Overburden.

Crater The bowl or basin-shaped depression in a volcano, which surrounds the vent from which eruptions take place. The mouth of a volcano. See also Caldera.

Craton A relatively rigid and stable region of the Earth's crust that has been relatively earthquake-free and not subject to deformation for a very long period of time. The relatively stable heart of a continent.

Crevasse A deep fissure or chasm in bedrock, a rock, or a glacier. The word, crevasse, was adapted from crevice to denote fissures or breaks too large for the idea represented by the word crevice. Crevasse is sometimes spelled Crevesse.

Crosscut A mining term to denote a horizontal opening from a shaft and at (or near) right angles to the vein or ore body. A crosscut provides access to the ore body. It is a horizontal opening running across the direction of the main workings. Also, a passageway or air course for ventilation purposes.

Crude Oil Also called petroleum or mineral oil, crude oil is a flammable, bituminous liquid mixture at normal atmospheric pressure containing countless numbers of chemicals compounds, primarily hydrocarbons, and relatively small amounts of sulfur, nitrogen, and oxygen in the form of derivatives of hydrocarbons. Some hydrocarbons are in gaseous form; others are liquids or solids Crude oil is found in natural underground reservoirs. It emerges from the earth along with varying degrees of water, gas, and other organic matter. Because of the below ground pressures, crude oil usually carries a considerable amount of natural gas in solution. Crude oil is formed by the decomposition of organic matter under pressure and over a great period of time.

Most crude oils contain a mixture of three series of compounds described as paraffins, naphthenes, and aromatics. The paraffin series is the broadest and extends from methane, which comprises natural gas, to the liquids that are refined into ordinary gasoline, to waxes. The naphthene series ranges from volatile liquids to tarry asphalts. The primary member of the aromatic series is benzene.

Various crude oils do not contain these in identical proportions. As a result, not all crude oils look alike, flow at the same rate, or have the same specific gravity. Some crudes are almost colorless, whereas others may be amber, brown, green, or pitch black. They may flow like water or creep like molasses. Crude oils containing relatively large amounts of sulfur are called sour crudes. Those having a fairly low sulfur content are called sweet crudes.

Crude oil serves as the raw material from which gasoline, jet fuel, heating oil, propane, petrochemicals, and other products are refined. It is separated into these and other valuable products during the refining process by fractional distillation or cracking.

Crusher A machine used to crush mined ore or other materials. The various types of crushers include the ball mill, hammer mill, gyratory crusher, and jaw crusher.

Crust The outermost layer of the Earth, consisting of relatively low-density rocks. The Earth's crust varies from about 6 miles to about 40 miles in thickness. It accounts for less than one percent of the Earth's volume. See also Core, Mantle.

Cubic Foot The common unit of measurement of gas volume. It is the volume of gas required to fill a space of one cubic foot at a normal atmospheric pressure of 14.73 pounds per square inch and a temperature of 60 degrees Fahrenheit. One cubic foot of natural gas contains an average of 1,027 BTUs.

Crystal A solid body having a characteristic, regularly repeating internal structure and enclosed by symmetrically arranged plane surfaces, intersecting at definite and characteristic angles. A solid formed by the solidification of a chemical and having a systematic internal arrangement of atoms that appears outwardly as a geometric solid with a surface consisting of symmetrical planes.

Cuesta A sloping plain or mesa top. A hill or ridge, which has one steep side and an opposite side, which slopes gently. See also Mesa

Cut-Off Grade The arbitrarily-defined, lowest grade of a mineral or ore, which will be mined from a deposit. It is the percentage grade at which recovery is considered to be economic. Consequently, it normally defines the boundary of the ore zone. The value of a cut-off grade is normally equivalent to the cost of mining.

Dacite A volcanic rock (or lava) that is similar to rhyolite, but has a lower silica content. It is fine-grained, typically light in color and has a silica content of approximately 65% and a moderate amount of sodium and potassium. Dacite is the extrusive equivalent of intrusive granodiorite

Dale A small valley.

Decay (Radioactive) The spontaneous disintegration of the nucleus of a radioisotope into two or more different particles and the simultaneous emission of alpha or beta and/or gamma rays. The end product is a less energetic, more stable nucleus. Each decay process has a definite half-life. The sum of the masses of the new particles is always less than the mass of the particle that disintegrated. For example, when an atom of polonium decays, an atom of lead is formed and an alpha particle is emitted. See also Half Life.

Decline An inclined shaft that connects to a working area underground in a mine.

Declivity A downward or descending slope and, particularly, a steep.

Defile A deep and narrow mountain pass between mountains.

Deformation A term for the folding and faulting of rock as a result of Earth forces, or the changes in rock that they produce

Delta A low-lying, triangular plain formed by the deposit of stream-borne sediments at the mouth of a river and enclosed by its diverging branches. The land bounded by the diverging branches at the mouth of the Nile River was perceived 2,500 years ago to have a deltoid shape. Consequently, the Greek letter known as delta was used to describe it. Although many deltas are deltoid or triangular in shape, exceptions occur. Consequently, the term is applied today to the exposed and submerged plain at a river's mouth, regardless of shape.

The delta building process is dynamic and may be likened to a contest between the river and the sea. The river and its system must supply and deposit stream-borne sediments more quickly than the waves and currents remove them.

Delta Plain The flat land area of a delta.

Dendrites Small branch marking on certain rocks or minerals due to the inclusion of a foreign material.

Density: The weight of a material per unit of its volume. It varies by mineral or substance. For example, gold's density is high, whereas the density of quartz is low.

Depletion The exhaustion, or using up, of a natural resource. For example, supplies of timber, oil, gas, and minerals are depleted when they are extracted or taken from the land. This reduces the company's natural assets over time.

The term, depletion, also denotes the allowance, which may be claimed by investors or corporations engaged in such ventures when calculating income tax. Like depreciation, it is intended to reduce taxable income in recognition of the eventual need to replace a wasting asset (the asset being used up). Limited partnerships, which invest in oil and gas, pass the depletion allowance on to their limited partners to use on their personal income tax returns.

Depletion is calculated in two different ways and the larger of the two results is deducted. Cost depletion merely amortizes the cost of oil property (leasehold cost) over its productive life. Percentage depletion is the lesser of 15% of the gross income from an oil and gas property or 50% of the net income from the property and is limited to 65% of the investor's taxable income from all sources. See also Crude Oil, Natural Gas, Petroleum.

Deposit A natural occurrence of a mineral or an ore or a body of rock containing valuable minerals. Also, any accumulation of sediment.

Deposition Any accumulation of material, by mechanical or chemical means, or by settling from water or air.

Derrick The steel tower erected vertically over a bore hole for the purpose of raising and lowering the drill pipe and other equipment into the well during drilling operations.

Desert Any large, arid region of sparse vegetation, which remains uncultivated due to a deficiency of moisture or barren soil. A desert is generally regarded as a desolate and barren region without water or trees and with little other plant growth. Areas, which have an annual precipitation of less than ten inches, are generally described as deserts.

Desertification The advance of desert conditions into an arid or semi-arid region due to climactic change, human influence, or both. The characteristics of desertification include a decrease in surface water, a lowering of the water table, salinization of topsoil and water, rising erosion, and a decline in native vegetation. The life-supporting capabilities of the land dwindle.

Desert Pavement A closely packed layer of rock fragments that is caused by the continual removal of loose, fine-grained material from the surface by the wind.

Detrital Sediment Sediment that is composed of the fragments of rock formed previously.

Detritus Loose rock fragments or particles that have resulted from the wearing down of rock.

Diamond A pure or nearly pure form of carbon, naturally crystallized in the isometric system, of extreme hardness. The diamond is the hardest of all minerals and the most brilliant of all precious gems. It has good cleavage parallel to the octahedron faces and is brittle.

Diatomite A siliceous, light-colored, sedimentary rock formed from the siliceous skeletons of diatoms

Diatreme A volcanic pipe consisting largely of breccia.

Dike A long, narrow, mass of igneous rock that cuts across an older rock into which it intrudes.

Diluvial Pertaining to a flood or deluge. A word derived from diluere, a Latin verb meaning to wash away.

Diluvion The gradual washing away of soil due to a flood or deluge. The opposite of Alluvium.

Diluvium A deposit of soil, sand, or gravel left by the retreat of a glacier or flood.

Diorite A dark, granular igneous rock consisting essentially of plagioclase feldspar and hornblende. Diorite is similar to gabbro, but not as dark, and containing less iron and magnesium. It is the plutonic equivalent of andesite.

Dip The angle by which a stratum or other geologic structure deviates from the horizontal plane of the earth's surface. It is measured downwards and in a plane perpendicular to the geologic structure (bed, vein, fault, etc.).

Dirt Earth or soil, especially if loose. Also, any filthy or unclean substrate, such as mud, grime, excrement, etc.

Discovery Well An exploratory well that encounters a previously untapped field of oil or gas.

Dissolution A form of chemical weathering by which minerals are leached from solid bedrock by a combination of water and acid and carried away.

Divide A mountain range, ridge, or area of high land separating the drainage system of one river from another. A watershed.

Dolomite A very common, white to pink colored, mineral. It consists of calcium magnesium carbonate (CaMgCO3) and occurs in crystals and cleavable or granular masses. It usually resembles both calcite and magnesite. It can be found almost wherever there is limestone.

Dolostone A sedimentary rock composed primarily of dolomite. It is believe that Dolostone formed as a magnesium replacement of limestone prior to lithification.

Dome In Geology, dome refers to a large or elliptical structure formed by the upward lifting of rock strata. It is a form of anticline, which slopes outward in all directions from its highest point. Impermeable shale covers a layer of permeable sandstone in some domes. This creates a natural trap for oil and gas migrating upward. In addition, dome describes the rounded summit of a hill or any geological feature resembling a dome. See also Anticline.

Doré Silver Crude silver that contains a small amount of gold after removing lead in a cupelling furnace.

Drainage Area The watershed of a stream or river system. Also called drainage basin. See also Watershed

Drift A deposit of detritus. Also, an approximately horizontal passageway in underground mining. Normally, it runs parallel to the vein or the length of the mineralized zone. Finally, the word is used for glacial drift, a term that describes rock, clay, sand, and silt that has been transported, and left behind, by a glacier.

Drift Mine A coal mine that is accessed by a passage excavated horizontally into the slope of a hill and into a coal seam.

Drilling The use of a machine to create holes in rock for removal of samples or loading with explosives.

Drilling Mud A mixture of clay, water, and additives that is used in drilling operations primarily in the oil and gas industry. The drilling mud circulates within the well and serves to lubricate and cool the drill-bit, carry rock cuttings to the surface, prevents the collapse of unstable strata into the hole, prevents the intrusion of water from water-bearing strata, and maintains pressure at the well bottom sufficient to avoid hydrocarbon blowout. The clay is usually bentonite.

Drill String The long drilling shaft consisting of the drill bit and the pipes connected end-to-end that the rotary table rotates and that provides a conduit for the drilling mud.

Drumlin An elongated, oval hill or mound of glacial debris. A drumlin slopes in the direction of the ice flow. It can be 400 to I2000 meters in length and 5 to meters high. A drumlin is also known as a Drum. See also Glacier

Dry Gas Natural gas that contains no water vapor.

Dry Hole A well that was drilled that did not provide commercial quantities of oil or gas.

Dry Wash See Arroyo

Dump A mechanism for overturning a freight car and unloading low-grade ore, rock, etc. A dump is often called a tipple. Also, the pile of ore so dumped.

Dune See Sand Dune.

Dry Wash See Arroyo

Earth Soil and dirt of all kinds. This includes gravel, clay, loam, and the like, in contrast to firm rock. See also Soil

Earthflow A stream or sheet of soil and rock material saturated with water and flowing down slope. An earth flow typically begins in a large basin on the upper part of a slope in which weathered materials accumulate. A heavy rainfall may cause movement. Its speed is affected by the amount of water present. An earth flow is a stage midway between a creep and a mudflow. See also Mudflow.

Earthquake A vibration or sudden undulation of an area of the earth's surface caused by the sudden release of tension between two shifting plates below a fault line. This vibration may appear as a violent shaking at the Earth's surface. See also Fault, Focus, Richter Scale, Seismograph, Seismology.

Ejecta Material that is ejected by a volcano, including pyroclastic material and lava bombs.

Element A basic substance of matter that cannot be divided into simpler substances by heating, cooling, or chemical means. It consists of a family of naturally occurring isotopes, all of which have the same atomic number and similar chemical properties. Metals comprise three quarters of all elements. Examples of elements include hydrogen, oxygen, carbon, iron, and gold. In contrast, neither water nor salt are elements because they contain two or more atoms having different atomic numbers. There are 115 known elements on Earth, of which 92 are naturally occurring. Each element is represented by different one- or two-letter abbreviations.

Eolian Pertaining to sand or rock material carried, arranged, or deposited by the wind.

Epicenter The point on the Earth's surface that is directly above an earthquake's hypocenter (focus). See Focus.

Epidote A family of silicate mineral that have the formula of calcium aluminum iron silicate and form green, stubby, prismatic crystals. It often occurs in veins or as a green coating on fracture surfaces. It is most common in metamorphic rocks. The epidote group is found as secondary minerals in low-grade regionally metamorphosed rocks.

Epigenetic Any ore that has been deposited later after formation of its host rock, for example a vein. The ore is younger than the host rocks.

Erosion The wearing away of land by the natural forces of nature, such as currents, tides, ocean, streams, winds or rain. Natural forces can gradually erode the soil and, over time, cause the loss of title to land. For example, an owner can experience loss to his interest in land if the sea is permitted to continue to encroach upon it.

Escarpment A high, steep, rock face of a cliff or ridge of notable length. An escarpment is created by erosion or faulting. If formed by faulting, it is often called a scarp, or a fault scarp if created by a fault. See Ridge

Eskar A glacial deposit in the form of a continuous, winding ridge, formed from the deposits of a stream flowing beneath the ice. An esker may be less than 100 meters in length or in excess of 500 kilometers. Its height can vary from three to 300 meters or more.

Estuary An inlet or arm of the sea through which the tide enters. An area in which the fresh water mixes with the salt water. See Tide

Evaporite See Halite.

Everglade A tract of low, swampy land, largely covered with tall grass and much of which is under water. The term is used, primarily, to denote a specific, large, area of south Florida. See also Swamp

Excavate To expose or lay bare by digging away the covering earth, sand, etc. To make a hole or cavity by digging. To hollow out by removing material from the inner part.

Excavation A hole or cavity made by excavating. Also, the act of excavating or site where excavating has been done.

Exploration The searching for and proving, or establishing the extent and value of, mineral deposits. This includes such activities as drilling and sampling.

Exploratory well A well drilled where petroleum has not been discovered previously, or a new well drilled to target formations above or below known reservoirs.

Extrusive Rock An igneous rock that was formed from lava that cooled and solidified rapidly at or near the Earth's surface.

Facies The composite nature of sedimentary rock that indicates the conditions and environment of its origin and that differentiate it from other rock.

False Bedrock: There are two definitions of false bedrock among miners; 1. Anything resembling or that can be mistaken for true bedrock. 2. A hard or relatively tight formation within a placer deposit, at some distance above true bedrock.

Fault A fracture in rock strata caused by movements of the Earth's crust. The strata on one side of the fracture are displaced in relation to the other. A fault is a fracture that divides rock or a vein into two sections, enabling one side to move relative to the other. See also Earthquake

Fault Block A section of rock that is separated from another by a fault.

Fault Zone An area of multiple faults. The fault zone may contain many small interlacing faults and may be hundreds or feet in width or more.

Feldspar Any of a group of minerals, principally aluminosilicates of potassium, sodium, and calcium, characterized by two cleavages at nearly right angles. Feldspars make up 60% of the Earth's crust. They are one of the most important constituents of igneous rocks and are also common in metamorphic and clastic sedimentary rocks. Feldspar crystals are stubby prisms, generally white, gray, or pink. The color can be white or pale shades of yellow, red, or green, and sometimes gray. Its luster is glassy. The hardness of all feldspars is 6 or close to it.

Felsic An adjective used to describe igneous rocks consisting chiefly of light-colored feldspars, feldspathoids, quartz, and other light-colored minerals. Felsic rocks are low in iron and magnesium.

Field A word used to denote a region characterized by a certain mineral. In particular, it is used to denote a set of rock strata containing hydrocarbons. Also, the surface area above a petroleum formation, including its installations for oil or gas production and treatment.

Fill Any material that is used to replace ore that has been mined in order to provide ground support.

Fine Gold A term used in reference to tiny particles of gold of the size that usually occur in gold deposits along gravel bars or outside of the bends in a waterway. There can be 12,000 such flakes per ounce. The term applies also to sand or any material that passes through a screen during a washing or other stage of a placer mining operation.

Fineness The proportion of pure precious metal in an alloy, often expressed in parts per thousand, or as a decimal. The term is frequently used in reference to the purity of a metal, such as gold or silver bullion. Natural gold is not normally discovered in pure form. It typically contains silver, copper, or another substance. Therefore, if the fineness of gold bullion is 0.995, one knows that pure gold accounts for 99.5% of the total weight of the bullion.

Fine Ounce A term used to describe one troy ounce of precious metal having no impurities. See Precious Metals, Troy Weight.

Fine Weight The weight of precious metal in a coin or bullion. This is calculated by multiplying the gross weight of the coin or bullion by its fineness. See also Bullion, Fineness.

Fiord A former glacial valley with steep walls and a U-shaped profile that is now occupied by the sea. A rocky inlet of the sea formed by the submergence of a glacial valley.

Fire Damp A combustible gas, methane, CH4, that is formed in mines by the decomposition of coal or carbonaceous matter. Also, an explosive methane-air mixture in which methane accounts for 5%-15% of the mixture.

Fissure An extensive, crack, break, or fracture in rock. An elongated crack. A fissure vein is a fissure that is filled with mineral matter.

Flat A tract of level ground or stretch of country without hills. Further, flat denotes an expanse of low ground through which a river flows. In addition, flat is used in reference to an extent of low ground covered by shallow water or over which the tide floods.

Float Loose and scattered fragments of ore, rock, etc., which have been broken off from an outcrop and moved to another by the action of wind, water, etc. Pieces of ore that have been separated from the parent vein by weathering.

Flood Plain A relatively flat stratified alluvium that borders a stream and is subject to inundation during floods, unless protected artificially. It is built up silt and sand carried out of the main channel during floods. Floodplains store excess water during periods of high water.

Flour Gold A term used to describe gold particles of extremely fine size; usually running 40,000 or more flakes per ounce. Flour gold is normally found near the surfaces of placer deposits and serves as a good indication of gold in the area.

Fools Gold Anything that can be mistaken for gold. Most of what is called fool's gold, is actually iron pyrite, a mineral consisting of iron sulfide. Other minerals occasionally mistaken for gold include biotite, chalcopyrite, marcasite, and pyrrhotite.

Footwall The top of the rock stratum beneath a vein or bed or ore.

Floatation The process for separating ore from gangue in which the metallic ore fraction rises to the top (or sinks to the bottom) of a bath and the gangue does the opposite. Flotation is a form of concentration in which the ore is powdered and then introduced to a bath of a given liquid. Chemical reagents create a froth in the liquid that causes some finely crushed minerals to float and the gangue to sink.

Flow Cleavage The cleavage due to the parallel alignment of the mineral's crystals when the rock was in a plastic condition.

Focus The precise point within the Earth's crust or mantle where rocks begin to rupture or move in an earthquake. Seismic waves radiate outward in all directions from this point. It is directly below the epicenter. Focus is synonymous with hypocenter. See Epicenter.

Fold Any bending or wrinkling of rock strata. Folds occur most commonly in sedimentary rocks.

Foliated Consisting of thin and separable laminate. A term to describe a layered structure

Foliation The arrangement of, or splitting up, of certain rocks or types of rocks in parallel, leaf-like layers that lie perpendicular to the flattened plane of a rock. Foliation occurs in metamorphic rocks on which directed pressure has been exerted. The pressure has elongated or squeezed flat minerals so that they become aligned. The sheet-like structure reflects the direction in which pressure was applied.

Footwall The top of the rock stratum on the underside of a vein or ore structure.

Foreshore That part of the shore which is under water at high tide and uncovered at low tide. A landowner owns absolutely to the high tide mark. However, the foreshore is subject to the rights of the public.

Fork The point at which a stream, river, road, or something else continuous in form, divides into two or more separately continued parts or branches. Also, any one of the separately continued branches (of a stream, for example).

Formation A body of rocks classed as unit for geological mapping. The body is of considerable extent and can be identified by distinctive characteristics and stratigraphic position. The rocks within the formation share characteristics, whether origin, age, or composition. The word, formation, also describes the process of depositing rock or mineral of a certain composition or origin.

Fossil The mineralized remains of plant or animal life that lived in a different geologic age. An impression, outline, or cast of any animal or plant that is preserved in rock after the original organic material has been replaced or transformed. Fossils can include both the hard parts and soft parts of plants and animals.

Fossil Fuel A nonrenewable energy source, such as oil, natural gas, or coal, which originates in decayed organic matter. Fossil fuels consist primarily of hydrocarbons.

Fossiliferous Bearing or containing fossils.

Fracture A crack or break in a rock. To break into random places, rather than to cleave, as do certain minerals.

Free Gold Gold discovered in a pure state in nature, as in placer mining. Goal that was not found in chemical combination with other minerals.

Friable Easily crumbled or reduced to powder. Crumbly. An adjective that is applicable to certain rocks and minerals.

Fumarole A hole in the ground or vent spring which emits steam or gaseous vapor of volcanic origin. Also spelled fumarol or fumerole.

Gabbro A dark, dense, coarse-grained, intrusive, igneous rock composed essentially of plagioclase feldspar and pyroxene. It is the intrusive equivalent to basalt.

Galena Native lead sulfide (PbS), a common heavy mineral. Galena is the chief ore of lead. It is a soft-blue gray mineral with lead-gray crystals, usually cubes and cleavable masses. It is widely distributed and occurs in many different types of deposits. Large deposits also occur as replacements of limestone or dolomite.

Gangue The waste rock or earthy material that surrounds a metal or mineral within an ore and which has no value. It must be separated from the mineral during processing. See also Flotation.

Gap A deep notch or ravine in a ridge or range of mountains or between hills. A pass or gorge.

Garnet Any of a group of hard, vitreous silicate minerals containing varying amounts of calcium, magnesium, iron, or manganese with aluminum or iron. The color varies with the composition, from colorless to yellow, red, violet, or green. A deep-red transparent variety garnet is used as a gem and as an abrasive. Garnets are typically found in metamorphic rocks, such as gneiss and schist.

Geiger Counter An instrument used to detect and measure radiation, although it cannot identify the type of radiation. It is a gas ionization detector that detects radioactivity by counting the formation of ions that it produces in a gas-filled tube when ionizing radiation passes through it. It is also called a Geiger-Müller detector.

Gemstone A precious stone that is suitable for cutting and polishing as a gem or gems. More than 2,000 minerals have been identified, but fewer than 100 are used as gemstones. However, there are only 16 important gemstones. They are: beryl, chrysoberyl, corundum, diamond, feldspar, garnet, jade, lazurite, olivine, opal, quartz, spinel, topaz, tourmaline, turquoise, and zircon.

Geode A hollow or partly hollow rock or nodular stone, often lined with crystals. Geodes are found in certain limestone beds and some shales. The common geode is a globe of up to one foot in diameter that has an exterior of chalcedony and an inner lining of inward projecting crystals. The crystals are usually quartz, but sometimes calcite or dolomite. A layer of calcite is often between the interior crystals the outer chalcedonic layer.

Geohydrology The science concerning the water below the surface of the Earth and the mechanics of its flow through rock. It is a field of study within the science of hydrology. Geohydrology is sometimes termed Hydrology or Groundwater Hydrology.

Geologic Time Scale Long before scientists were able to assign ages in years to rock formations, they were able to tell the correct sequence of formations by using relative dating principles and fossils. Consequently, over time, they were able to construct a geologic time scale, using increasingly more sophisticated methods to date rock formations.

The time scale of 4.55 billions years of geologic time scale is divided into two great expanses of time. The Precambrian Eon began when Earth first formed 4.55 billion years ago and ended about 570 million years ago. The Phanerozoic Eon began 570 million years ago and continues today. In turn, the eons were subdivided into eras and, then, into periods.

The Precambrian Eon consists of the Hadean, Archean, and Protozoic Eras. The Phanerozoic Eon consists of the Paleozoic, Mesozoic, and Cenozoic Eras.

The Paleozoic Era is subdivided into the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian Periods.

The Mesozoic Era is subdivided into the Triassic, Jurassic, and Cretaceous Periods.

The Cenozoic Era is subdivided into the Tertiary Period (Palocene, Eocene, Oligocene, and Miocene Epochs) and the Quarternay Period (Pleistocene and Holocane Epochs). The present epoch is the Holocane Epoch.

Geologist A person who specializes in the study of the structure, composition, and history of the earth's crust, conducting research into various rock strata, fossil records, and geologic features.

Geology Science devoted to the study of the structure and evolution of materials that form the earth's crust, including the physical properties of rocks and minerals.

Geomorphology The branch of geology and geography that is concerned with the description, formation, and classification of the Earth's land forms and their relationship to underlying structures

Geophysics The branch of geology that studies the physics of the Earth. The field of study that involves measuring the Earth's shape, gravity, and magnetic field, and the flow of electrical particles through its atmosphere, as well as tectonic activity and the formation of large new features in the earth's crust. It finds use in mining exploration tot detect zones that are distinguished by their physical properties, such as electromagnetic conductivity, magnetism, etc.

Geyser A natural hot spring from which intermittent jets of steam, hot water, or mud are expelled in a fountain-like column by an accumulation of steam. See also Spring

Glacial Valley Any stream valley, which has been eroded by a glacier. When a glacier is not permitted to spread out, but is confined to a valley, it tends to deepen and widen the valley floor. Typically, the valley is left with a U-shaped cross section, which may be thousands of feet in depth and miles in length. Glacial erosion may cause the walls of the valley to become almost vertical. In addition, the walls may bear striations caused by passing boulders carried by the glacier. See also Glacier, Hanging Valley, Kame

Glacier Any large mass of perennial ice, which forms on land and moves forward under its own weight. A glacier may resemble a large field or stream of ice flowing slowly down a valley or slope at the rate of a few inches per day. Often, it is several miles in length. Glaciers are formed high in the mountains and in other areas where winter snowfall exceeds what melts during summer. They are created gradually as snow continues to fall and compact. Eventually, a glacier begins to move under its own weight. It descends until it reaches an air temperature in lower altitudes sufficient to cause melting at a rate, which overcomes any further advance.

Gneiss A coarse-grained metamorphic rock, generally made up of alternating bands of light and dark-colored minerals, some bands being rich in feldspar and quartz, with others rich in hornblende or mica.

Gold (Au) A rare chemical element, gold is a precious, dense, bright yellow and lustrous metal. It is a good conductor of heat and electricity, and is the most malleable and ductile of metals. It is soft, does not tarnish or corrode, and is workable. Gold is the most malleable and ductile of metals. One ounce of gold can be hammered into a thin translucent wafer covering more than 100 square feet. Alternatively, one ounce of gold can be drawn into a wire 50 miles in length. Gold has a specific gravity of 19.3 making it also one of the heaviest metals known. The weight of one cubic foot of gold would be 1,206 pounds. Its melting point is 1,063 degrees C (1,945 degrees F). This metal is found in relatively pure form in nature and was one of the first metals to attract man's attention.

Gold can be found in very small amounts in all igneous rocks. It occurs mostly in the native state, remaining chemically uncombined, except with tellurium and possibly selenium and bismuth. The world's production of gold is about 2,000 tons per year. The holdings accumulated during all recorded history is about 120,000 metric tons. This would occupy the volume of a 60-feet cube.

When used for jewelry, gold is usually alloyed with silver, palladium, or platinum. The gold content of these alloys is expressed in karats. Pure gold is 24-karat; a 50% gold alloy would be 12-karat. The contract size of gold at the COMEX is 100 troy ounces. The contract size for Kilo gold at the Chicago Board of Trade is one kilogram (32.15 troy ounces). .

Gold/Silver Ratio The current spot price of one ounce of gold expressed as the number of ounces of silver providing the same value. That is, the number of ounces of silver it takes to purchase one ounce of gold at current spot prices. This is calculated by dividing the price of gold by the price of silver, whether both are expressed in dollars per troy ounce or dollars per kilogram.

Gold Dust: The particles and flakes of gold obtained in placer mining. The word is commonly used for unsorted particle sizes, generally anything under #16 mesh.

Gorge A very rugged, narrow, and deep ravine, particularly one which has a stream flowing through it. A ravine that has walls of rock. See also Barranca, Gap, Pass

Gossan A rust-colored deposit of mineral matter at the outcrop of a vein or ore body that is caused by the weathering of pyrite.

Grab Sample A rock sample that has collected at random and is not necessarily representative of the body of rock.

Grade The amount of lead, zinc, or other metal in a rock sample, usually given as a percentage of weight. If the concentrations is very low, as with gold, silver, or platinum, the concentration may be given in grams per tonne (g/t) or ounces per ton (opt). The grade is the standard used to judge the quality of a mineral, metal or commodity. The term, grade, is also used to denote slope, inclination, or gradient. See Gradient.

Gradient The degree of inclination of a slope, grade, etc. Slopes or gradients are expressed as ratios. The ratio is calculated by dividing the length of rise by the length of run. A ratio of 1:10 may be termed 10 percent. A ratio of 1:20 is 5 per cent.

A slope of 1:50 (2%) is usually not difficult for walking. A slope of (1:20) 5 per cent is noticeable and is somewhat difficult. A slope of 1:10 (10 per cent) is noticeably steep and difficult for walking. A slope of (1:3) 33 per cent requires steps.

Grain The smallest unit of weight in most systems, a grain was originally based on the weight of a grain of wheat. The unit, which appears in the troy system of weights, is sometimes used to express the weight of gold. There are 480 grains in a troy ounce and 15.432 grains to a gram. See also Precious Metals, Troy Weight.

Grain Size The size of individual mineral crystals or particles in a rock or deposit.

Granite A coarse-grained, intrusive, hard igneous rock commonly found everywhere in mountainous regions. It is typically light in color. The rock consists mainly of quartz, feldspar, and mica. The principal ingredient is feldspar. Granite has more orthoclase feldspar than plagioclase feldspar.

Granite is the plutonic equivalent of rhyolite. It is the most common plutonic rock of the Earth's crust and is formed by the cooling of magma at depth. Granite typically forms irregular masses of varying size, ranging from less than a few miles in maximum dimension to much larger masses (batholiths).

Granitic Similar in appearance to granite.

Granodiorite An intrusive igneous rock that is similar to granite in formation, occurrence, composition, and appearance, but darker in color and containing more plagioclase.

Granulite A metamorphic rock composed of granular minerals of uniform size, as quartz, feldspar, or pyroxene, and showing a definite banding.

Graphite A soft crystalline form of carbon that appears in black to dark gray foliated masses with a metallic luster and a greasy feel. Graphite appears naturally in metamorphic rocks, such as marble, schist, and gneiss. It is used in a wide variety of applications. Graphite is also called Plumbago, Black Lead.

Gravel Small and somewhat rounded water-worn stones and pebbles as they occur naturally, or a mixture of these with coarse sand. Gravel generally constitutes a good coarse aggregate because of its hardness. If gravel is used for this purpose, the individual stones and pebbles comprising it should be approximately the same size as crushed stone.

Greywacke A quartz sandstone that has a significant content of mud and silt. It is sometimes called dirty sandstone.

Greenstone A useful field name for any fine-grained, greenish rock of igneous origin.

Groundwater Free water below the surface of the land. Its source is rain or melting snow, which seeps into the earth below. As this moisture penetrates the soil, it fills porous rock, and creates a saturated zone. The upper surface of this zone is known as the water table. Groundwater continues to descend until it eventually reaches a zone of impermeable rock. Wells drilled or dug to provide water must extend below the water table in order to draw from these water-bearing porous rock, sand, or gravel formations termed aquifers. Natural outflows of groundwater occur through springs and river beds. Droughts of brief duration do not seriously deplete groundwater supplies.

Groundwater Hydrology See Geohydrology.

Groundwater Table See Water Table

g/t The abbreviation of grams per tonne. See also Ton.

Gulch A deep and narrow ravine with steep, but smoothly inclined, slopes cut out by a rushing stream. See Ravine

Gypsum A common, soft, white mineral consisting of hydrated calcium sulfate. It occurs in crystals and masses, soft enough to be scratched by the fingernail. Gypsum is found in extensive beds associated with other evaporite minerals (e.g., anhydrite and halite) in sedimentary formations. It is deposited from ocean brine and also occurs in quantity in saline lakes and salt pans. Gypsum is a common sulfate mineral of commercial importance. Its many applications include use in sheet rock for construction.

Halite Rock salt. A soft, highly soluble, white or colorless mineral that occurs in cubical crystals with perfect cleavage. Naturally occurring sodium chloride (NaCl). Halite is found in sedimentary rocks of many ages, particularly with limestone, dolomite, and shale. It is termed evaporite because it forms deposits due to the evaporation of salt water in partially enclosed basins.

Hallmark An official mark or stamped impression on the surface of a bar of precious metal to indicate a standard of purity. It indicates the producer, serial number, weight, and purity of metal content. Hallmarks are used in marking gold or silver. Fineness, Precious Metal.

Hammock See Hummock

Hanging Wall A mass of rock overhanging a fault plane. Also, the surface of the country rock that is in contact with the upper surface of an ore body.

Hanging Valley A high glacial valley, which is intersected at a noticeable elevation by the side of a larger valley or sea cliff.

Hardness The resistance of a mineral to scratching. This indicates the strength of the bonds that hold the mineral's atoms together. A mineral's hardness of a mineral is measured by scratching it against another substance of known hardness. The resistance to scratching or abrasion is expressed in terms of a scale that was devised in 1812 by Friedrich Mohs, a German mineralogist. The hardness of a mineral is determined by observing whether its surface is scratched by substances of known hardness. Mohr's scale of known mineral hardness is composed of 10 minerals that have been the following given arbitrary hardness values. In ascending order of hardness, they are: talc (1), gypsum (2), calcite (3), fluorite (4), apatite (5), orthoclase (6), quartz (7), topaz (8), corundum (9), diamond (10). Additional hardness values include the fingernail (2+), a copper coin (about 3), a pocketknife blade (5+), window glass (5½), and a steel file (6½).

Hardrock Mining The mining of igneous or metamorphic rocks. Sometimes called lode mining.

Head Frame A structure erected over a mine shaft to support the hoist rope pulley and equipment necessary for raising and lowering equipment and personnel.

Hectare A measure of land area in the metric system equal to 10,000 square meters or 100 ares. It is also equal to 2.471 acres in British Imperial and U.S. Customary measure. Hectare derives from "hect," a contraction of the Greek word for hundred, and from the Latin word, "area." See also Are, Land Measure.

Hematite The chief iron ore. Ferric Oxide is a natural iron oxide that is red or brown in color (brick-red when powdered) and has an iron content of 70%. Hematite is heavy and relatively hard. It is the most common iron ore. The name, hematite, comes from the Greek word for blood.

There are many forms of hematite, some of which have different names. Some varieties have steel-gray crystals and a brilliant metallic luster. Others have a reniform surface (kidney ore) or a fibrous structure (pencil ore). However, a great deal of hematite is in a soft, fine-grained, earthy form called red ochre or ruddle. Hematite has been discovered as an accessory mineral in many igneous rocks. Nevertheless, the most important deposits of hematite are sedimentary.

High Grade The ore that is richest in the values that are sought. The best ore. An ore of a grade sufficiently high to provide for a profitable mining operation.

As a verb, high grade has two meanings. One meaning is to selectively mine the best ore in a deposit. The second meaning is to steal ore or precious metals, as by a miner from a mine.

High Grading The stealing or pilfering of high-grade ore or nuggets from workings of a hard rock or placer mine by employees or others.

Highland High, elevated land, such as a plateau, or mountainous extent of land. Also, a lofty cliff, promontory, or headland, or pertaining to a hilly or mountainous region. See also Uplands

Hillock A mound or small hill. See also Knoll

Hogback A steep-sided ridge running parallel to adjoining mountains and caused by unequal erosion on the edges of tilted strata. See also Ridge

Horizon A particular plane in a vertical section of rock strata that represents the deposit of a specific period. It is distinguish by special features, such as distinctive fossil species. Hornblende Any of the common black or greenish aluminous varieties of amphibole. Hornblende forms the major part of the heavy, dark, basic rock, diorite, and is also a common ingredient of the light colored rocks, such as granite and gneiss. See Amphibole.

Hornblende Schist A variety of schist that contains needles of hornblende, which lie in parallel planes.

Hornfels A hard, dark-colored, very fine-grained metamorphic rock produced by the intrusion of magma into shale or basalt.

Horst A block of rock that lies between two parallel faults and has moved upward in relation to the rocks on either side of the faults.

Host Rock The rock in which minerals or the ore deposit occurs.

Hot Spring A term denoting a Thermal Spring. See Spring, Thermal Spring

Hummock A thickly wooded and often elevated tract of land. Also, a low mound of earth or rock or an elevated piece of ground rising from a swamp. A hillock or knoll. Also spelled hammock. See also Hillock, Knoll

Hyaloclastite A deposit caused by lava shattering into small angular fragments as it flows into water.

Hydrocarbons Any of a class of organic compounds composed of hydrogen atoms and carbon atoms in various combinations. The carbon atoms join together to form the spine or framework of the compound. The hydrogen atoms attach to the carbon atoms in differing configurations. Hydrocarbons are the principal constituents of petroleum and natural gas and the basis of all petroleum products. Those hydrocarbons, which have few carbon atoms in their molecules, are gaseous at room temperature. Methane, ethane, and propane are examples. In contrast, those hydrocarbons which have molecules containing many carbon atoms are solid at room temperature. Those having an intermediate number of carbon atoms in their molecules are liquid. Hydrocarbons serve as fuels and lubricants as well as raw materials for the production of plastics, rubbers, fibers, explosives, solvents, and industrial chemicals. See also Crude Oil, Natural Gas.

Hydrometallurgy The process of extracting metals by leaching ore with liquid solvents. The usual operations are leaching or dissolution of the metal or metal compound in water, separation of the waste, and precipitation of the metal or one of its pure compounds from the leach solution. Dilute sulfuric acid is a common leaching agent.

Hydrophone Acoustical sensor used to detect sources of sound under water or receive reflected waves during seismic exploration at sea.

Hydrothermal Of, or relating to, hot, aqueous solutions, which may carry ions of metals and other compounds in solution, within the Earth's crust or on the Earth's surface.

Hydrothermal Ore Deposit A mineral body formed by the precipitation of metallic ions from hot mineral-laden water. The hydrothermal solution originates, it is believed, in the heating by magma of water that circulates deep below the earth's surface.

Hydrous Containing water. The word applies to minerals or other substances that contain water in a kind of union, as in hydrates or hydroxides.

Hypocenter The focus of an earthquake. See Focus.

Igneous Rock Any of various types of rock formed by the cooling of magma (molten rock) to form solid matter. molten lava. Igneous rocks form one of the three main classes of rocks. The other two are metamorphic and sedimentary rocks.

If the igneous rock is formed within the Earth's crust, it is termed intrusive. If it flows out onto the surface of the earth before solidifying, it is termed extrusive.

Igneous rocks below the Earth's surface may occur as batholiths, bosses, laccoliths, and veins. They include granite, syenite, diorite, gabbro, and peridotite.

The hypabyssal intrusive rocks, igneous rocks formed at a moderate distance below the earth's surface, may occur as dykes, sills or other similar small bodies. They include porphyry, porphyrite, diabase, and lamprophyre.

The extrusive igneous rocks, those formed at the Earth's surface, typically are formed as lava flows cool. They include obsidian, perlite, rhyolite, trachyte, andesite, basalt, and tephrite.

Although the various types of igneous rocks vary greatly in composition, less than a dozen groups of minerals account for most of them. These are quartz, feldspars, pyroxenes, amphiboles, micas, olivines, nephelinite, leucite, and apatite.

Ignimbrite Rock formed by the widespread deposition and lithification of volcanic ash volcanic breccia.

Incline An entry to a mine that is neither vertical nor horizontal, but too steep for use of a belt conveyor.

Index Fossil A fossil of an organism that is known to have lived during a relatively short and known period and can therefore be used to date the rock in which it is found.

Indicated Mineral Resource That portion of a Mineral Resource for which quantity and grade can be estimated with a confidence sufficient to evaluate the economic feasibility of extracting the mineral(s). The estimate is based on sampling sufficient to confirm the extent and grade of the mineral resource.

Inferred Mineral Resource That portion of a Mineral Resource for which quantity and grade can be estimated on the basis of geological information on hand and limited sampling, although there has been no verification. The conclusion is that extraction is economically feasible.

Injection well A well that is used to injecting water or gas into a formation in order to maintain the field pressure an attempt to increase the petroleum recovery rate.

Intrusion An igneous rock body that has forced its way in a molten state into surrounding country rock. Also, the igneous rock mass so formed within the surrounding rock. Dikes, sills, and batholiths are intrusions. Intrusive rock An igneous rock formed by the entrance of magma into preexisting rock.

Iron Sand A sand rich in iron ore, such as magnetite or ilmenite.

Joint A narrow crack that divides a rock and along which neither side has visibly moved. Joints typically appear in parallel sets.

Kaolin A fine, soft, white clay, also called China Clay, that is used in the manufacture of china and porcelain and other products. The natural material consists principally of the mineral kaolinite, which is usually found in whitish clay-like masses and consists of aluminum silicate. It has a dull luster, its crystals are of microscopic size, and it is characterized by a greasy feel. Kaolinite is a secondary mineral resulting from the decomposition of by weathering of feldspar, the calcium, potassium, and sodium having been replaced by water.

Karat A unit of measurement of the purity (fineness) of gold. The purity of a gold alloy is expressed as a number of karats. Pure gold is known as 24-karat. It has at least 999 parts of gold per thousand. An alloy of 16 parts of gold and 8 parts of an alloying material is termed 16-karat gold. It has 666 parts per thousand. A 50:50 mixture of gold and an alloying material would be called 12-karat gold. (A gold carat is a 1/24th part, or 4.1667 percent of the whole.) Karat is spelled carat outside of the United States. However, it should not be confused with the unit of measurement for the weight of gems, which is also called carat. See also Bullion, Fineness, Gold.

Karst An area of limestone or dolomite formations that is characterized by closed depressions, sinkholes, caves, subterranean passages, and processes of subsidence and collapse.

Kettle A steep-sided, bowl-shaped depression formed in glacial deposits commonly without surface drainage. A kettle is typically formed when a large block of ice, which subsequently melts, is partially or wholly buried in the drift.

Kilogram (kg) The basic metric unit of mass and weight equal to the mass of a platinum-iridium cylinder kept at the International Bureau of Weights and Measures near Paris and nearly equal to 1000 cubic centimeters of water at the temperature of its maximum density.

Kimberlite A variety of mica peridotite that is composed of olivine and biotite. It is low in silica and high in magnesium. Kimberlite is characteristic of South African diamond mines.

Knob A prominent peak, which has a rounded summit. Alternatively, an isolated rounded hill or mound. A knoll. See Knoll.

Knoll A small, rounded hill or hilltop. A hillock. See Hillock.

Kyanite A blue to light green mineral consisting of aluminum silicate in crystalline form, which forms in metamorphic rocks.

Continue to L - Z

Science Glossaries

editing service main page
editing service site map