How Is Kyanite Formed?
Kyanite, a Polymorph
Kyanite is one of the three polymorphs of Al2SiO5; the other two are anadlusite and sillimanite. Although these polymorphs have the same chemical composition, they differ by the way they are formed and their crystalline structure. Kyanite is formed through high pressure conditions, and is the densest of the Al2SiO5 polymorphs. Kyanite has a closely packed crystalline structure for this reason. It is also a metamorphic mineral found in schists, gneisses and granite pegamatites.
Kyanite, also known as disthene, munkrudite and cyanite, can give clues to the terrain structure of where it forms. Often times, kyanite forms where there is high pressure due to the regional metamorphosis of an area. Kyanite forms in aluminous rocks where quarts veins dissect through, as long as the pressure is adequate. Other associated minerals are muscovite, biotite, staurolite and corundum. It can also occur with the presence of kimberlite.
Properties
Kyanite can have a perfect cleavage and has a hardness index of about five parallel to the crystal length on the Mohs scale. When it is perpendicular, the hardness index is 7 to 7.5. The variety in hardness depends on the crystallographic direction.
The crystalline structure of kyanite is easily recognized by its flat bladed shape. According to W.R.Hamilton, A.R.Woolley and A.C.Bishop's "The Hamlyn Guide to Minerals, Rocks, and Fossils," kyanite can take the form of radiating bladed aggregates. Kyanite has a triclinic crystal structure and is symmetrical. There are three axes of varying length and they do not form right angles to the other axes.
Colors
"Kyanite" is derived from the Greek word "kyanos" for "blue." The blue in kyanite is due to Fe+2 and Ti+4. Other impurities can contribute to the blue color. Light blue colors are due to chromium found in kimberlite structures. Other colors of kyanite include black, light green and green, yellow and grey. Kyanite has darker tints toward the center of the crystal with paler tints toward the edges. Kyanite also ranges from transparent to translucent.
Uses
Kyanite is used in ceramics, porcelain and spark plugs. Kyanite is also used as an index mineral to gauge the temperature, depth and pressure of terrain in metamorphism. It is also used as a collector's mineral and more vibrant colors of kyanite are used as gemstones. Throughout history Kyanite has had metaphysical properties, including usage with meditation and tranquility. It also been used with opening and aligning the body's chakras. Kyanite has been associated with psychic awareness.
Tags: crystalline structure, Kyanite also, also used, hardness index, high pressure