Kyanite

Kyanite
General
CategoryNesosilicate
Formula
(repeating unit)
Al2SiO5
IMA symbolKy[1]
Strunz classification9.AF.15
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H-M symbol)
Space groupP1
Unit cella = 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
ColorBlue, white, rarely green, light gray to gray, rarely yellow, pink, orange, and black, can be zoned
Crystal habitColumnar; fibrous; bladed
TwinningLamellar on {100}
Cleavage[100] perfect [010] imperfect with 79° angle between
FractureSplintery
TenacityBrittle
Mohs scale hardness4.5–5 parallel to one axis
6.5–7 perpendicular to that axis
LusterVitreous to white
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.53–3.65 measured; 3.67 calculated
Optical propertiesBiaxial (-); high relief
Refractive indexnα = 1.712 – 1.718 nβ = 1.720 – 1.725 nγ = 1.727 – 1.734
Birefringenceδ = 0.012 – 0.016
PleochroismTrichroic, colorless to pale blue to blue
2V angle78°–83°
References[2][3][4]

Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks generally indicates metamorphism deep in the Earth's crust. Kyanite is also known as disthene or cyanite.[5]

Kyanite is strongly anisotropic, in that its hardness varies depending on its crystallographic direction. In kyanite, this anisotropism can be considered an identifying characteristic, along with its characteristic blue color. Its name comes from the same origin as that of the color cyan, being derived from the Ancient Greek word κύανος. This is typically rendered into English as kyanos or kuanos and means "dark blue."

Kyanite is used as a raw material in the manufacture of ceramics and abrasives, and it is an important index mineral used by geologists to trace metamorphic zones.

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ "Kyanite" (PDF). Handbook of Mineralogy. 2001. Archived from the original (PDF) on 2019-05-08. Retrieved 2018-01-01.
  3. ^ "Kyanite". MinDat. Retrieved 2013-06-14.
  4. ^ "Kyanite Mineral Data". Webmineral.com. Retrieved 2013-06-14.
  5. ^ Jackson, Julia A., ed. (1997). Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute. ISBN 0922152349.