gabbro

SRI Petrography ID: 20

Dakota Mahagoni
USA

Names

[de] Gabbro
[en] gabbro

Description

Medium to coarse grained, medium to dark green, sometimes nearly black igneous rock, containing only 0-5 % quartz.
Main mineral content: high-calcium plagioclase feldspar and pyroxene (mostly clinopyroxene), olivine.
Gabbro is mostly found in large intrusive bodies of island arc environments and ophiolites in connection to basalt as surface equivalents.

Color

medium to dark, nearly black

Grain Size

Medium to coarse grained

Texture

Granular texture

Minerals

high-calcium plagioclase feldspar (about 50%) and pyroxene (about 50%), as an alteration product of pyroxene during the late stages of crystallisation often biotite and hornblende are formed.

Occurences

various large occurences all over the world. E.g. Germany, South Africa, India, Greenland, Turkey, Italy, Greece

Comments

Gabbro is also called norite
Plutonic equivalent to basalt
Diabase (or dolerite) is a fine grained gabbro containing granular pyroxene and randomly oriented laths of plagioclase, formed by faster cooling in dikes and sills. A variety of Diabase is the slightly metamorphic basalt in the Alps.

Classification

Class

IGNEOUS ROCKS

Broader Terms

coarse-grained crystalline rocks

Narrower Terms

African-gabbro

Austria-gabbro

Canada-gabbro

Czech-Republic-gabbro

France-gabbro

Italy-gabbro

Norway-gabbro

Russia-gabbro

Sweden-gabbro