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Glossary of Terms


(adapted from AGI's "Glossary of Geology")


Rock: Any naturally formed material composed of one or more minerals having some degree of chemical and mineralogic constancy.

Mineral: A naturally formed chemical element or compound having a definite chemical composition and, usually, a characteristic crystal form.

Sediment: Solid fragmental material, or a mass of such material, that originates from weathering of rocks and is transported by, suspended in, or deposited by air, water, or ice, or that is accumulated by other natural agents, such as chemical precipitation from solution or secretion by organisms, and that forms in layers on the Earth's (or other planet's) surface in a loose, unconsolidated form; e.g., sand, gravel, silt, mud.

Limestone: A sedimentary rock consisting chiefly of the chemical calcium carbonate, primarily in the form of the mineral calcite (more rarely, aragonite).

Dolostone: A carbonate sedimentary rock consisting chiefly of the chemical calcium-magnesium carbonate, primarily in the form of the mineral dolomite, or approximating the mineral dolomite in composition, or a variety of limestone or marble rich in magnesium carbonate.

Clay: (a) A rock or mineral fragment or a detrital particle of any composition (often a crystalline fragment of a clay mineral), smaller than a very fine silt grain, having a diameter less than 1/256 mm. (b) A loose, earthy, extremely fine-grained, natural sediment or soft rock composed primarily of clay-size or colloidal particles and containing a considerable amount of clay minerals (hydrous aluminum silicates).

Shale: A fine-grained, indurated, sedimentary rock formed by the consolidation of clay, silt, or mud, and characterized by very thin layers, and by a composition with an appreciable content of clay minerals, and commonly with a high content of quartz sediment.

Sandstone: A medium-grained sedimentary rock composed of abundant fragments of sand size, more or less firmly united by a cementing agent; the consolidated equivalent of sand, intermediate in texture between conglomerate and shale.

Sand: (a) A rock fragment or particle smaller than a granule and larger than a coarse silt grain, having a diameter in the range of 1/16 to 2 mm. (b) A loose aggregate of unconsolidated mineral or rock particles of sand size.

Gravel: An unconsolidated, natural accumulation of rock fragments resulting from erosion, consisting predominantly of particles larger than sand (diameter greater than 2 mm), such as boulders, cobbles, pebbles, granules, or any combination of these.

Calcite: The most common crystalline or mineral form of calcium carbonate; a common rock-forming mineral.

Barite: The crystalline or mineral form of barium sulfate.

Gypsum: A widely, distributed mineral consisting of hydrous calcium sulfate; it is the most common sulfate mineral.

Fluorspar (fluorite): The crystalline or mineral form of calcium fluoride.

Sphalerite: A crystalline or mineral form of zinc-iron sulfide.

Galena: A crystalline or mineral form of lead sulfide.

Saltpeter: Naturally occurring potassium nitrate.

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 Last Updated: Tuesday, 08-Sep-2009 12:00:08 Eastern Daylight Time