Gabbro

Thin lamina of a gabro seen under the petrographic microscope with polarized light. The minerals of grey tones to black with banded maclas are plagioclase and the most colorful are clinopiroxeno and olivino.

In its strict sense, gabbro is a plutonic igneous rock composed mainly of calcium plagioclase and pyroxene in similar volume proportions. In a broader sense, gabbro can refer to the gabroic rocks of the QAPF diagram, that is, those in the anorthosite-gabro-diorite field that have more than 10% dark minerals and calcium plagioclase (An50-An100).

Gabbro sensu stricto is the plutonic equivalent of basalt, but unlike basalt the mineralogy of gabbro is much more variable.

Gabbro sensu strico and lato can be found in various tectonic environments such as: mid-oceanic ridges, subduction zones, continental rifts, and oceanic islands. Gabbro is traded as a construction material under the name "black granite". gabbros and ultramafic rocks. There are also vanadium mineralizations associated with gabbro.

Gabbro takes its name from the Italian town of Gabbro in Tuscany.

Mineralogy and chemistry

Gabbros can be classified, depending on whether they contain added minerals of plagioclase and pyroxene, into:

1. Gabro (sensu stricto), rock composed of plagioclase with augita (clinopiroxeno variety) and sometimes with olivino
2. Hyperite, rock composed of plagioclase with augita and hyperstena (ortopiroxene variety) and sometimes with olivino
3. Norita, rock composed of plagioclase with hyperstena and sometimes with olivino
4. Evjita, rock composed of plagioclase with hornblenda
5. Bojita, rock composed of plagioclase with hornblenda and augita
6. Troctolite, rock composed mainly of olive and plagioclase.

Additionally, if a gabbro contains more than 5% by volume of olivine it is called olivine gabbro and if it contains more than 5% quartz, quartz gabbro.

Gabbro may also contain apatite, magnetite, or ilmenite as accessory minerals.