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Kyanite
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 also includes the Polymorphism (materials science)|polymorph andalusite and the polymorph sillimanite. Kyanite is strongly anisotropy|anisotropic, in that its Mohs scale of mineral hardness|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.
At temperatures above 1100 °C, kyanite Chemical decomposition|decomposes into mullite and Fused quartz|vitreous silica via the following reaction: 3(Al2O3·SiO2) → 3Al2O3·2SiO2 + SiO2. This transformation results in an expansion.Uses of kyanite
Kyanite is used primarily in refractory and ceramic products, including porcelain plumbing fixtures and dishware. It is also used in Insulator (electrical)|electrical insulators and abrasives. Kyanite has been used as a gemstone, though this use is limited by its anisotropism and perfect cleavage. Kyanite is one of the index minerals that are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism. Finally, as with most minerals, kyanite is a collector's mineral.
Associated minerals
Kyanite is usually found in association with its polymorphs, as well as other silicate minerals. These include:
- andalusite, Al2SiO5
- sillimanite, Al2SiO5
- quartz, SiO2
- staurolite, Fe2Al9Si4O22(OH)2
- micas, AB2-3(X, Si)4O10(O,F,OH)2
- garnets, A3B2(SiO4)3
Alternative names
Kyanite has several alternative names, including disthene, munkrudite and cyanite. White-grey kyanite is also called rhaeticite.
Notes for identification
Kyanite's elongated, columnar crystals are usually a good first indication of the mineral, as well as its color (when the specimen is blue). Associated minerals are useful as well, especially the presence of the Polymorphism (materials science)|polymorphs or staurolite, which occur frequently with kyanite. However, the most useful characteristic in identifying kyanite is its anisotropism. If one suspects a specimen to be kyanite, verifying that it has two distinctly different hardnesses on perpendicular axes is a key to identification.
References
- WebMineral Listing
- MinDat Listing
- Mineral Galleries
- Catalog Mineralov
Category:Gemstones
Category:Aluminium minerals
Category:Nesosilicates
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Sources: StartLearningNow, Wikipedia | Usage license: GNU FDL
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