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
Anthracite is a type of sedimentary rock which is hard and is variety of coal that has high luster
From Greek anthrakites, from anthrax, anthrak meaning coal
Coarse Grained Rock, Fine Grained Rock, Medium Grained Rock, Opaque Rock