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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
Novaculite is a dense, hard, fine-grained, siliceous metamorpic rock which is a type of chert that breaks with conchoidal fracture
From Latin word novacula, for razor stone
Fine Grained Rock, Opaque Rock