Definition
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Etymology
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Hornfels is a metamorphic rock formed by the contact between mudstone or other clay rich rock, and a hot igneous body, and represents a heat altered equivalent of the original rock
From German which means hornstone
Fine Grained Rock, Opaque Rock
Pumice is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals
From Old French pomis, from a Latin dialect variant of pumex
Durable Rock, Medium Hardness Rock
Fine Grained Rock, Opaque Rock