|KYANITE, SILLIMANITE AND ANDALUSITE|
Kyanite, whose name derives from the Greek word kyanos, meaning blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. Kyanite is a diagnostic mineral of the Blueschist Facies of metamorphic rocks.
Kyanite is a member of the aluminosilicate series, which includes the polymorph andalusite and the polymorph sillimanite. Kyanite is strongly anisotropic, in that its hardness varies depending on its crystallographic direction. While this is a feature of almost all minerals, in kyanite this anisotropism can be considered an identifying characteristic.
Kyanite is usually found in association with its polymorphs, as well as other silicate minerals. These include:
|Sillimanite also called Bucholzite is an alumino-silicate mineral with the chemical formula Al2SiO5. Sillimanite is one of three alumino-silicate polymorphs, the other two being andalusite and kyanite. A common variety of sillimanite is known as fibrolite, so named because the mineral appears like a bunch of fibres twisted together when viewed under thin section or even by the naked eye. Both the fibrous and traditional forms of sillimanite are common in metamorphosed sedimentary rocks. It is an index mineral indicating a high degree of metamorphism.|
|Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. The variety chiastolite commonly contains dark inclusions of carbon or clay which form an X or a cross in section. Andalusite is a common regional metamorphic mineral which forms under low pressure and moderate to high temperatures. The minerals kyanite and sillimanite are polymorphs of andalusite, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. Because of this the three minerals are a useful tool to help identify the pressure-temperature paths of the host rock in which they are found. It was first reported from Andalucia, Spain in 1789.|
|SILLIMANITE IN INDIA|
|There are large resources of sillimanite in beach sands from where granular sillimanite is recovered. The reserve position is adequate to meet the requirements. There is shortage of lumpy sillimanite for which exploration efforts need to be intensified. Search for sillimanite will be taken up in Maharashtra to establish the continuity beyond the mining area.|