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feldspare-porphyry

feldspare-porphyry

SRI Petrography ID: 28

Names

[de] Feldspat-Porphyr
[en] feldspare-porphyry

Description

Porphyry is volcanic rock composed of large, conspicuous crystals (phenocrysts) embedded in a fine grained to glassy groundmass. Since the term “porphyry” refers only to the texture of the rock and not to its composition, the expression “porphyritic rock” is often used.
Porphyry is very variable, the dfferent types are named by the character of the phenocrysts in the groundmass. They are found in main classes of igneous rocks, especially in basalt, andesite, granite, rhyolite, syenite, diorite, gabbro, and peridotite.
Porphyritic felsites and basalts are widely distributed. The porphyritic texture indicates two separate stages of solidification.
Feldspar-porphyry is a porphyry witch contains large feldspar phenocrysts.

Color

Dark coloured, feldspar phenocrysts white, grey or pink

Grain Size

Fine grained matrix, coarse grained phenocrysts

Texture

porphyric

Minerals

phenocrysts: feldspar (plagioclase, alkali-feldspar)

Classification

Class

IGNEOUS ROCKS

Broader Terms

porphyric (inequigranular) crystalline rocks