Definition
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Etymology
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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
Scoria is a dark-colored extrusive igneous rock with abundant round bubble-like cavities
From late Middle English (denoting slag from molten metal), from Greek skōria refuse, from skōr dung
Durable Rock, Medium Hardness Rock
Fine Grained Rock, Opaque Rock