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
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism
From Old French esclate, from esclat (French éclat)
Durable Rock, Medium Hardness Rock
Fine Grained Rock, Opaque Rock