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Asbestos

A silicate mineral whose thin, strong fibers separate readily. Used in heat resistance. Known for causing terminal respiratory illness

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Arsenic

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

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Arrastra

A primitive milling process whereby ore is placed in a round, rock lined pit and milled by a series of blocks or crushers, suspended by beams radiating from the centre of the pit

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Autogenous grinding

The grinding of ore in a rotating cylinder using larger pieces of usually homogenous ore to grind down smaller pieces into finer grades

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Arkose

Sandstone with high feldspar content, usually coarse-grained and pink to red

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Argon

A monatomic, inert, colourless gas. Symbol, Ar. Used in light bulbs and fluorescent tubes