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Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers called coal beds
From the Old English term col, which has meant mineral of fossilized carbon since the 13th century
Coarse Grained Rock, Fine Grained Rock, Medium Grained Rock, Opaque Rock
Ignimbrite is a volcanic rock consisting mainly of pumice fragments, formed by the consolidation of material deposited by pyroclastic flows
From Latin ignis fire + imber, imbr- shower of rain, storm cloud + -ite
Durable Rock, Medium Hardness Rock
Fine Grained Rock, Opaque Rock