Porphyritic rock consisting of phenocrysts of quartz and alkali feldspar (usually orthoclase) embedded in a microcrystalline or cryptocrystalline groundmass; a rock of this kind.
Origin
Late 18th century. After German quarziger Porphyr.
Definition of quartz porphyry in US English:
quartz porphyry
noun
Geology
Porphyritic rock consisting of phenocrysts of quartz and alkali feldspar (usually orthoclase) embedded in a microcrystalline or cryptocrystalline groundmass; a rock of this kind.
Origin
Late 18th century. After German quarziger Porphyr.