Kyanite


Kyanite
Kyanite
General
Category Silicate mineral
Chemical formula Al2SiO5
Crystal symmetry Triclinic pinacoidal H–M Symbol: 1 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
Crystal system Triclinic
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, whose name derives from the Greek word kuanos sometimes referred to as "kyanos", meaning deep blue, 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 4 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]

Contents

Uses of kyanite

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.

Notes for identification

Deep blue kyanite

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 of 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.

Occurrence

Kyanite occurs in gneiss, schist, pegmatite, and quartz veins resulting from moderate to high-pressure regional metamorphism of principally pelitic rocks. It occurs as detrital grains in sedimentary rocks. It occurs associated with staurolite, andalusite, sillimanite, talc, hornblende, gedrite, mullite and corundum.[1]

Phase diagram of the Aluminosilicates.[6]

References


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Look at other dictionaries:

  • Kyanite — Ky a*nite, n. See {Cyanite}. [1913 Webster] …   The Collaborative International Dictionary of English

  • kyanite — [kī′ə nīt΄] n. a bluish silicate of aluminum, Al2SiO5, that forms in long, thin, bladed crystals that are found in metamorphic rocks …   English World dictionary

  • kyanite — /kuy euh nuyt /, n. a mineral, aluminum silicate, Al2SiO5, occurring in blue or greenish bladed triclinic crystals, used as a refractory. Also, cyanite. [1785 95; irreg. < Gk kýan(os) CYAN + ITE1] * * * or cyanite or disthene Silicate mineral,… …   Universalium

  • Kyanite — Disthène Disthène Catégorie IX : silicates Cristaux de disthène …   Wikipédia en Français

  • kyanite — Cyanite Cy a*nite ( n?t), n. [See {Cyanic}.] (Min.) A mineral occuring in thin bladed crystals and crystalline aggregates, of a sky blue color. It is a silicate of aluminium. [Written also {kyanite}.] [1913 Webster] …   The Collaborative International Dictionary of English

  • kyanite — distenas statusas T sritis chemija formulė Al₂[O|SiO₄] atitikmenys: angl. disthene; kyanite rus. дистен; кианит ryšiai: sinonimas – kianitas …   Chemijos terminų aiškinamasis žodynas

  • kyanite — n. a blue crystalline mineral of aluminium silicate. Derivatives: kyanitic adj. Etymology: Gk kuanos dark blue * * * kyanite variant of cyanite, now more usual …   Useful english dictionary

  • kyanite — noun Etymology: German Zyanit, from Greek kyanos dark blue enamel, lapis lazuli Date: 1794 an aluminum silicate mineral Al2SiO5 that occurs usually in blue thin bladed triclinic crystals and crystalline aggregates …   New Collegiate Dictionary

  • kyanite — noun a blue neosilicate mineral, AlSiO, found in metamorphic rocks …   Wiktionary

  • kyanite — n. cyanite, bluish green almost colorless silicate mineral …   English contemporary dictionary


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