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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
Basalt is a common extrusive igneous rock formed by the rapid cooling of basaltic lava exposed at or very near the surface of Earth
From Late Latin Basaltes (variant of basanites ), very hard stone, which was imported from Ancient Greek Basanites
Durable Rock, Medium Hardness Rock
Fine Grained Rock, Opaque Rock