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quartz-porphyry

quartz-porphyry

SRI Petrography ID: 27

Bozner
Südtirol

Names

[de] Quarz-Porphyr
[en] quartz-porphyry

Description

Porphyry is a volcanic rock composed of large, conspicuous crystals (phenocrysts) and 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.
There exist many varieties of porphyry, the specimens 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, syenite, diorite, gabbro, and peridotite.
Porphyritic felsites and basalts are widely distributed. The porphyritic texture indicates two separate stages of solidification. The porphyritic texture is common in extrusions, e.g., lava, dykes.
Quartz porphyry contains large quartz phenocrysts

Color

matrix grey or pink, quartz phenocrysts appear grey

Grain Size

Fine grained to glassy matrix, coarse grained phenocrysts

Texture

porphyric

Minerals

phenocrysts: quartz, feldspar

Occurences

worldwide in volcanic environments, e.g. South Tyrol (“Bozner Quarzporphyr”), Egypt

Classification

Class

IGNEOUS ROCKS

Broader Terms

porphyric (inequigranular) crystalline rocks

Narrower Terms

Czech-Republic-quartzporphyry

France-quarzporphyry