Anorthosite

ANORTHOSITE (from the French word "anorthose" (plagioclase) * EN: anorthosite, plagioclasite, plagioclase rock; DE: Anorthosit; FR: anorthosite; ES: anortosita; RU: анортозит) is the rock of the group of gabbro, which is consisting mainly of the calcium-rich calcareous-alkaline feldspar, usually of labrador (labradorite), less often of andesite or bytownite, with small content (not more than 5-10%) of the coloured minerals (olivine, pyroxene, titanomagnetite, apatite, and others). The colour is from white to dark gray, sometimes there may be found almost black varieties (on the account of admixture of ilmenite and other finely dispersed ore minerals), the average chemical composition of anorthosite (% of mass) is: SiO2 is 50.41; TiO2 is 0.18; Al2O3 is 27.75; Fe2O3 is 0.89; FeO is 1.61; MnO is 0.06; MgO is 1.54; CaO is 12.23; Na2O is 3.17; K2O is 0.86; H2O is 1.13; P2O5 is 0.17. The density of anorthosite is 2710-3050 kilograms per cubic metre, the porosity is 0.2-0.5%, the water absorption is 0.1-0.3%, the resistance to compression is 100-250 megapascals.

Anorthosite

They distinguish stratiform anorthosites, which may be found in the form of the separate layers within the differentiated massifs of various ages, and autonomous pre-Cambrian anorthosites, which are forming large bodies (with area of several thousand square kilometres) within the basement of the ancient platforms. They distinguish according to the age the anorthosites of the early stages of development of the Earth (2-4 billion years), and anorthosites of the stage of stabilization of the ancient platforms (1.7-2 billion years). The latter ones form the giant anorthositic belt, which is framing the East European Platform from the west. Autonomous anorthosites associate with gabbro, granulites, charnockites, and rapakivi granites.

Anorthosites are one of the most ancient known rocks within the Earth's crust. Besides this, the analogs of the terrestrial anorthosites have been found on the Moon within the composition of the Lunar soil, which has been delivered to the Earth. It is assumed, that anorthosite is one of the first products, which have crystallized within the crust of the Earth; this event has served as the start of the entire subsequent evolution of rocks of the Earth's crust. The massifs of anorthosites may be found within all regions of outcrops of most ancient rocks to the daylight surface. Within the USSR, there are known outcrops of anorthosites within the Kola peninsula, Ukraine, Latvia and Eastern Siberia, the huge massif is within the Dzhugdzhur ridge within Primorye.

Anorthosites may be used as the building and facing stone. Large deposit of anorthosites is being developed within Ukraine (Korostensky pluton). Sometimes anorthosites within isolated places are beneficiated with titanomagnetite and apatite, and may serve as the titanium or phosphoric ore.