Kyanite

Kyanite
Kyanite crystals.jpg
General
Category Nesosilicate
Formula
(repeating unit)
Al2SiO5
Strunz classification 9.AF.15
Crystal system Triclinic
Crystal class Pinacoidal (1)
(same H-M symbol)
Space group P1
Unit cell a = 7.1262(12) Å
b = 7.852(10) Å
c = 5.5724(10) Å
α = 89.99(2)°, β = 101.11(2)°
γ = 106.03(1)°; Z = 4
Identification
Color Blue, white, rarely green, gray, yellow, pink, orange, and black, can be zoned
Crystal habit Columnar; fibrous; bladed
Twinning Lamellar on {100}
Cleavage [100] perfect [010] imperfect with 79° angle between
Fracture Splintery
Tenacity Brittle
Mohs scale hardness 4.5-5 parallel to one axis
6.5-7 perpendicular to that axis
Luster Vitreous to pearly
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.53 - 3.65 measured; 3.67 calculated
Optical properties Biaxial (-)
Refractive index nα = 1.712 - 1.718 nβ = 1.720 - 1.725 nγ = 1.727 - 1.734
Pleochroism Trichroic, colorless to pale blue to blue
2V angle 78°-83°
References [1] [2] [3]

Kyanite is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. Kyanite in metamorphic rocks generally indicates pressures higher than four kilobars. Although potentially stable at lower pressure and low temperature, the activity of water is usually high enough under such conditions that it is replaced by hydrous aluminosilicates such as muscovite, pyrophyllite, or kaolinite. Kyanite is also known as disthene, rhaeticite and cyanite.

Kyanite is a member of the aluminosilicate series, which also includes the polymorph andalusite and the polymorph sillimanite. Kyanite is strongly anisotropic, in that its hardness varies depending on its crystallographic direction. In kyanite, this anisotropism can be considered an identifying characteristic.

At temperatures above 1100 °C kyanite decomposes into mullite and vitreous silica via the following reaction: 3(Al2O3·SiO2) → 3Al2O3·2SiO2 + SiO2. This transformation results in an expansion. [4]

Its name comes from the same origin as that of the color cyan, being derived from the Ancient Greek word κύανος. This is generally rendered into English as kyanos or kuanos and means "dark blue".

Uses

Kyanite is used primarily in refractory and ceramic products, including porcelain plumbing fixtures and dishware. It is also used in electronics, electrical insulators and abrasives.

Kyanite has been used as a semiprecious gemstone, which may display cat's eye chatoyancy, though this use is limited by its anisotropism and perfect cleavage. Color varieties include recently discovered orange kyanite from Tanzania.[ citation needed] The orange color is due to inclusion of small amounts of manganese (Mn3+) in the structure. [5]

Kyanite is one of the index minerals that are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism.

Other Languages
العربية: كيانيت
asturianu: Cianita
azərbaycanca: Kianit
български: Кианит
català: Cianita
čeština: Kyanit
Deutsch: Kyanit
eesti: Küaniit
Ελληνικά: Κυανίτης
español: Cianita
Esperanto: Kianito
euskara: Zianita
فارسی: کیانیت
français: Disthène
한국어: 남정석
हिन्दी: क्यानाइट
hrvatski: Kianit
Bahasa Indonesia: Kyanit
italiano: Cianite
עברית: קיאניט
ქართული: კიანიტი
қазақша: Кианит
lietuvių: Kianitas
magyar: Kianit
Nederlands: Kyaniet
日本語: 藍晶石
norsk nynorsk: Kyanitt
oʻzbekcha/ўзбекча: Kianit
polski: Kyanit
português: Cianite
română: Disten
русский: Кианит
slovenčina: Kyanit
slovenščina: Kianit
srpskohrvatski / српскохрватски: Kianit
suomi: Kyaniitti
svenska: Kyanit
українська: Кіаніт
Tiếng Việt: Kyanit