Definition
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Chert is a hard, dark, opaque sedimentary rock which is composed of silica with an amorphous fine-grained texture
From flint-like quartz, 1670s, of unknown origin- a local term, which has been taken into geological use
Fine Grained Rock, Opaque Rock
Peridotite is a dense, coarse-grained plutonic is the main constituent of the earth's mantle
From French, from peridot + -ite
Durable Rock, Medium Hardness Rock
Coarse Grained Rock, Opaque Rock