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Aqua regia

A corrosive, noxious, yellow liquid made with nitric and hydrochloric acids, usually one part nitric acid and three parts hydrochloric acid. Used in efficiently dissolving and processing gold and platinum

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Andesite

A type of grey to black volcanic rock composed mostly of silica, plus iron and magnesium

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Appalachian orogeny

Late Paleozoic Era diastrophism with possible origin in Late Devonian Period, continuing until the end of the Permian Period. A mountain forming period for deposits in the Appalachian and Cordilleran geosynclines

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Aplite

Light-colored igneous rock characterized by fine-grained saccharoidal texture, ranging in composition from gabbro to granite, consisting of quartz, potassium feldspar, and high acid plagioclase

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Aphanitic

The texture of igneous rock in which crystalline components are too small to be detected visually by the unaided eye. Syn. Cryptocrystalline

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Apex

The top or terminal edge of 2 or more points of a geological structure

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Apatite

A hexagonal or monoclinic pseudohexagonal mineral with the general formula A5(XO4)3(F,Cl,OH) , where A = (Ba,Ca,Ce,K,Na,Pb,Sr,Y) and X = (As,C,P,Si,V). Calcium Phosphate

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Arsenic

A steel-gray and brittle metal. Symbol, As. Highly poisonous