![]() Muscovite + staurolite + quartz → biotite + kyanite + H 2O However, under these conditions, the reactions that produce kyanite, such as: Kyanite is potentially stable at low temperature and pressure. ![]() By contrast, the metamorphic zones surrounding the Fanad pluton of Ireland, which formed by contact metamorphism at a shallower depth in the crust, include andalusite and sillimanite zones but no kyanite zone. Barrow was characterizing a region of Scotland that had experienced regional metamorphism at depth. Barrow defined kyanite zones and sillimanite zones in his pioneering work on the mineralogy of metamorphic rocks. Kyanite is often used as an index mineral to define and trace a metamorphic zone that was subject to a particular degree of metamorphism at great depth in the crust. This makes the presence of kyanite in a metamorphic rock an indication of metamorphism at high pressure. They are all equally stable at the triple point near 4.2 kbar and 530 ☌ (986 ☏). Kyanite is the most stable at high pressure, andalusite is the most stable at lower temperature and pressure, and sillimanite is the most stable at higher temperature and lower pressure. There are two polymorphs of kyanite: andalusite and sillimanite. Minerals with identical compositions but a different, distinct crystal structure are called polymorphs. ![]() Kyanite is one of the most common minerals, having the composition Al 2SiO 5. It is associated with staurolite, andalusite, sillimanite, talc, hornblende, gedrite, mullite and corundum. It occurs as detrital grains in sedimentary rocks, although it tends to weather rapidly. Kyanite is also occasionally found in granite and pegmatites and associated quartz veins, and is infrequently found in eclogites. ![]() Kyanite occurs in biotite gneiss, mica schist, and hornfels, which are metamorphic rocks formed at high pressure during regional metamorphism of a protolith which is rich in aluminium (a pelitic protolith). There is no direct linkage between the silica tetrahedra, making kyanite a member of the nesoilicate class of silicate minerals. The aluminium octahedra form chains along the length of the crystal, half of which are straight and half of which are zigzag, with silica tetrahedra linking the chains together. The kyanite structure can be visualized as a distorted face centered cubic lattice of oxygen ions, with aluminium ions occupying 40% of the octahedral sites and silicon occupying 10% of the tetrahedral sites. Thus, a steel needle will easily scratch a kyanite crystal parallel to its long axis, but the crystal is impervious to being scratched by a steel needle perpendicular to the long axis. It typically forms sprays of bladed crystals, but is less commonly found as distinct euhedral (well-shaped) crystals, which are particularly prized by collectors. It is typically patchy blue in color, though it can range from pale to deep blue and can also be gray or white or, infrequently, light green. Kyanite is an aluminum silicate mineral, with the chemical formula Al 2SiO 5. Kyanite within quartz, Hunterian Museum, Glasgow Kyanite is used as a raw material in the manufacture of ceramics and abrasives, and it is an important index mineral used by geologists to trace metamorphic zones. This is typically rendered into English as kyanos or kuanos and means "dark blue." Its name comes from the same origin as that of the color cyan, being derived from the Ancient Greek word κύανος. In kyanite, this anisotropism can be considered an identifying characteristic, along with its characteristic blue color. Kyanite is strongly anisotropic, in that its hardness varies depending on its crystallographic direction. Kyanite is also known as disthene or cyanite. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks generally indicates metamorphism deep in the Earth's crust. Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. Trichroic, colorless to pale blue to blue perfect imperfect with 79° angle between Blue, white, rarely green, light gray to gray, rarely yellow, pink, orange, and black, can be zoned
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