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Quartz-porphyry
Quartz-porphyry, in petrology, is the name given to a group of hemi-crystalline acid rocks containing porphyritic crystals of quartz in a more fine-grained matrix which is usually of micro-crystalline or felsitic structure. In the hand 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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