Definitions

porphyry

porphyry

[pawr-fuh-ree]
porphyry, igneous rock composed of large, conspicuous crystals (phenocrysts) and a groundmass in which the phenocrysts are embedded. Some authorities consider the expression "porphyritic rock" better usage than porphyry, since the term refers only to the texture of the rock—not its chemical, physical, or mineralogical composition or color. The texture is important in the determination of the circumstances under which the rock formed. The phenocrysts vary in size; the groundmass may be either glassy or made up of coarse or fine granules or crystals. The varieties of porphyry are many, the specimens being named by the character of the phenocrysts in the groundmass. They are found in main classes of igneous rocks, e.g., in granite, syenite, diorite, gabbro, and peridotite. Porphyritic felsites and porphyritic basalts are widely distributed. The porphyritic texture indicates two separate stages of solidification. In the first phase the phenocrysts form in the molten mass; in the second, the molten mass itself crystallizes into a solid. Porphyritic texture is especially common in extrusions, e.g., in lava.

A large body of igneous rock, having distinct crystals in a relatively fine-grained base, that contains chalcopyrite and other sulfide minerals. These deposits contain vast amounts of ore that averages a fraction of 1percnt copper by weight; although low-grade, the deposits are important because they can be worked on a large scale at low cost. Large porphyry copper deposits are worked in the southwestern U.S. (where molybdenum may be produced as a by-product), the Solomon Islands, Canada, Peru, Chile, Mexico, and elsewhere.

Learn more about porphyry copper deposit with a free trial on Britannica.com.

Porphyry (pronounced /'pɔː(ɹ)fɪri/, from the Greek Πορφύριος porphyrios "purple-clad") may refer to:

See also

Search another word or see porphyryon Dictionary | Thesaurus |Spanish
Copyright © 2014 Dictionary.com, LLC. All rights reserved.
  • Please Login or Sign Up to use the Recent Searches feature
FAVORITES
RECENT

;