Porphyry

Porphyry: an extrusive igneous rock composed mainly of Feldspars, Quartz, and Mica; color ranges from gray to brown. It has a “porphyritic” texture, meaning it contains prominent Quartz and Feldspar crystals, often corroded within a fine-grained groundmass. Porphyries are classified as either Quartz-bearing or Quartz-free. Quartz-bearing porphyries correspond compositionally to Rhyolites-Dacites, while Quartz-free porphyries correspond to Trachytes.

back to the gemological glossary