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Late-stage charnockite dykes cutting anorthosite, Rogaland, Norway Job Charnock's Mausoleum at St John's Church compound, Kolkata. Charnockite (/ ˈ tʃ ɑːr n ə k aɪ t /) is any orthopyroxene-bearing quartz-feldspar rock formed at high temperature and pressure, commonly found in granulite facies’ metamorphic regions, sensu stricto as an endmember of the charnockite series.
The chain silicate structure of the pyroxenes offers much flexibility in the incorporation of various cations and the names of the pyroxene minerals are primarily defined by their chemical composition. Pyroxene minerals are named according to the chemical species occupying the X (or M2) site, the Y (or M1) site, and the tetrahedral T site.
Jadeite is a pyroxene mineral with composition Na Al Si 2 O 6.It is hard (Mohs hardness of about 6.5 to 7.0), very tough, and dense, with a specific gravity of about 3.4.It is found in a wide range of colors, but is most often found in shades of green or white.
Diopside is a monoclinic pyroxene mineral with composition MgCaSi 2 O 6. It forms complete solid solution series with hedenbergite (FeCaSi 2 O 6) and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class.
Hedenbergite has a number of specific properties. Its hardness is usually between five and six with two cleavage plains and conchoidal fracture. Color varies between black, greenish black, and dark brown with a resinous luster. Hedenbergite is a part of a pyroxene solid solution chain consisting of diopside and augite, and is the iron rich end ...
Purely pyroxene-bearing volcanic rocks are rare, restricted to spinifex-textured sills, lava tubes and thick flows in the Archaean greenstone belts.Here, the pyroxenite lavas are created by in-situ crystallisation and accumulation of pyroxene at the base of a lava flow, creating the distinctive spinifex texture, but also occasionally mesocumulate and orthocumulate segregations.
Euhedral crystal of augite from Teide (4.4 x 3.0 x 2.3 cm). Augite is a solid solution in the pyroxene group. Diopside and hedenbergite are important endmembers in augite, but augite can also contain significant aluminium, titanium, and sodium and other elements.
Some forms of actinolite are used as gemstones. One is nephrite, one of the two types of jade (the other being jadeite, a variety of pyroxene). [5] Another gem variety is the chatoyant form known as cat's-eye actinolite. This stone is translucent to opaque, and green to yellowish green color. This variety has had the misnomer jade cat's-eye ...