Keyite

Keyite is a mineral with the chemical formula Cu2+3Zn4Cd2(AsO4)6 · 2H2O.[2] The name comes from Charles Locke Key (born 1935), an American mineral dealer who furnished its first specimens.[3] Keyite is monoclinic-prismatic, meaning its crystal form has three unequal axes, two of which have 90° angles between them and one with an angle less than 90°.[3] Keyite belongs to the biaxial optical class, meaning it has more than one axis of anisotropy (optic axis), in which light travels with zero birefringence, and three indices of refraction, nα = 1.800, nβ, and nγ = 1.870.[5][4] Being a very rare cadmium copper arsenate, keyite is only found in Tsumeb, Namibia in the Tsumeb mine, a world-famous copper mine known for its abundance of rare and unusual minerals.[3]

Keyite
Keyite on adamite (greenish)
General
CategoryArsenate minerals
Formula
(repeating unit)		Cu2+3Zn4Cd2(AsO4)6 · 2H2O
IMA symbolKey[1]
Strunz classification8.CA.50
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupI2/a
Unit cella = 11.654(3) Å
b = 12.780(5) Å
c = 6.840(3) Å
β = 99.11°; Z = 2
Identification
Formula mass1,520.19 g/mol
Colorazure/ blue
Crystal habitprismatic, tabular
Cleavagegood (001) cleavage
Mohs scale hardness3.5 - 4
Streaklight blue
Diaphaneitytranslucent
Density5.106g/cm3
Optical propertiesbiaxial
Refractive indexnα = 1.800, nβ, and nγ = 1.870
Birefringence0.070
Pleochroismx: pale blue, y: greenish blue, z: deep blue
References[2]

[3]

[4]

References
  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. Fleischer, M., Cabri, L.J., and Pabst, A. (1977) New Mineral Names. American Mineralogist, 62, 1259.
  3. Cooper, M.A.; Hawthorne, F.C. (1996). "The crystal structure of keyite, Cu32+Zn4Cd2(AsO4)6(H2O)2, an oxysalt mineral with essential cadmium". Canadian Mineralogist. 34: 623–630. Retrieved 22 May 2022.
  4. Keyite, WebMineral.com, retrieved 22 May 2022
  5. Keyite, Mindat.org, retrieved 22 May 2022


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