Amphibolite

AMPHIBOLITE (EN: amphibolite; DE: Amphibolit; FR: amphibolithe; ES: Amphiboliteanfibolita; RU: амфиболит) is the dark-coloured metamorphic rock, which is consisting mainly of alumina-rich amphibole (hornblende), plagioclase (andesine), and sometimes garnet.

Amphibolites are formed during the regional and contact metamorphism of the moderate and high grades within the conditions of the amphibolitic facies of the deepness. The texture of amphibolite is massive, foliated or linear. The structure is granoblastic, nematoblastic, or fibroblastic, and also there exist all gradual transitions between the amphibolite with these types of textures and structures. The lamination is caused, as a rule, by the oriented situation of hornblende and biotite. Within the varieties, which are containing small quantity of mica, the lamination may be difficult to discern. Amphibolites are formed on the account of the source rocks of the very diverse composition: most often from the erupted rocks of the basic (gabbro, diabase, basalt) composition, less often on the account of the ultrabasic erupted rocks, of the sediments of the marly composition, and also of the tufas and tufagenic sedimentary rocks.

The nomenclature of amphibolite is conducted according to the characteristical minerals, with respect to which they distinguish the biotite, garnet, quartz, kyanite, scapolite, zoisite, epidote, and others. Amphibolite may be found within the USSR within the regions of the development of the metamorphic rocks, most often of the pre-Cambrian age (Baltic, Ukrainian, Aldan shields, Northern Tien Shan, and others). The density of amphibolite is 2900-3150 kilograms per cubic metre, the porosity is 0.1-0.34%, the resistance to compression is 81-264 megapascals.

They use amphibolites as the building stone (raw material for the crushed gravel); the black varieties of amphibolite are ornamental and facing stones. The requirements of the industry for the quality of amphibolite in order to make the crushed gravel are the same as for the entire group of the erupted and metamorphic rocks (see the "Granite" article). Amphibolite usually does not form large deposits; its development is performed together with the host rocks, namely, gneisses, granite-gneisses (the Musozero deposit within the Murmansk province, Pokrovskoe deposit within the Arkhangelsk province, and others).