Quartz-porphyry, in
petrology, is the name given to a group of hemi-
crystalline acid rocks containing
porphyritic crystals of
quartz in a fine-grained
matrix, usually of micro-crystalline or
felsitic structure. In specimens, the quartz appears as small rounded, clear, greyish,
vitreous blebs, which are crystals, double
hexagonal pyramids, with their edges and corners rounded by resorption or corrosion.
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