Definition
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Etymology
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Other Categories
Porphyry is a reddish-brown to purple igneous rock containing large phenocrysts of various minerals embedded in a fine-grained matrix
From Old French porfire, from Italian porfiro and in some cases directly from Latin porphyrites
Fine Grained Rock, Opaque Rock
Arkose is a sedimentary rock, specifically a type of sandstone containing at least 25% feldspar
From Auvergne region of France used by a French geologist Alexandre Brongniart in 1826 who applied this term to some feldspathic sandstones
Coarse Grained Rock, Opaque Rock