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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
Siltstone can be defined as a fine-grained sedimentary rock which mainly consists of consolidated silt
From English word silt and stone and from Proto-Indo-European root sal and stainaz
Fine Grained Rock, Opaque Rock