Kyanite Kyanite Kumquat Category="Gemstones"Category="Silicate minerals"

Kyanite
[image]
General
CategoryMineral
Chemical formula Al2SiO5
(aluminium silicate)
Identification
Color Blue; also green, white, grey, black
Crystal habit Columnar; fibrous
Crystal system Triclinic
Cleavage[100] Perfect, [010] Imperfect
FractureBrittle
Mohs Scale hardness 4.5-5 parallel to one axis
6.5-7 perpendicular to that axis
LusterVitreous; Pearly
Refractive index1.71 - 1.75
PleochroismTrichroic, colorless to pale blue to blue
StreakWhite
Specific gravity3.56 - 3.67
Melting point
SolubilityNone
DiaphaneityTransparent to translucent

Kyanite, whose name derives from the Greek, kyanos, meaning blue, is a typically blue Silicate Mineral, commonly found in Aluminium-rich metamorphic pegmatites and/or Sedimentary rock.

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.

Uses of kyanite

Kyanite is used primarily in refractory and ceramic products, including porcelain plumbing fixtures and dinnerware. It is also used in electrical insulators and abrasives. Kyanite is important enough an ore that a mining company, the Kyanite Mining Corporation focuses on its processing and refinement. Kyanite has also been used as a gemstone, though this use is limited by its anisotropism and perfect cleavage. 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:

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 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