Zaïrite

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Zaïrite
Zairite-520947.jpg
Zaïrite from Eta-Etu, Kivu, Democratic Republic of Congo (Zaïre), (field of view 6 mm)
General
Category Phosphate minerals
Formula
(repeating unit)
Bi(Fe3+,Al)3[(OH)6|(PO4)2]
Strunz classification 8.BL.13
Crystal system Trigonal
Crystal class Hexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space group R3m
Unit cell a = 7.015, c = 16.365 [Å]; Z = 3
Identification
Formula mass 646.86 g/mol
Color Greenish, greenish white, yellow green.
Cleavage None observed
Fracture Irregular, uneven
Tenacity Brittle
Mohs scale hardness 4.5
Luster Vitreous, resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 4.37
Optical properties Uniaxial(-)
Refractive index nω = 1.820 - 1.830 nε = 1.810
Birefringence δ = 0.0100-0.0200
References [1][2][3]

Zaïrite is a phosphate mineral with the chemical formula Bi(Fe3+,Al)3[(OH)6|(PO4)2].[1] The name was given from where it was locally discovered in Eta-Etu, Kivu, Congo (Zaïre) in 1975.[2]

Properties[edit]

Zaïrite crystallizes in the trigonal crystal system, which means it contains three equal horizontal axes with angles of 120° between them.[4] The mineral has a trigonal-hexagonal scalenohedron shape.[5] Zairite belongs to the uniaxial optical class. It means the light and vibrations passing through the mineral only has one direction it follows and it travels at the same speed.[4]

Occurrence[edit]

The mineral was first described from the Eta-Etu district, northern Kivu Province, Democratic Republic of the Congo (then Zaire) usually in the weathering areas of quartz wolframite deposits where it occurs with native bismuth, bismutite, quartz and mica.[3] Zaïrite is found in granite pegmatites, which are igneous coarse-grained rocks. It has also been reported from Kreuzberg Mountain in Upper Palatinate, Bavaria, Germany.[1]

References[edit]

  1. ^ a b c Mindat.org
  2. ^ a b Webmineral data
  3. ^ a b Handbook of Mineralogy
  4. ^ a b Klein, C., Dutrow, B. (2007) The 23rd edition of the Manual of Mineral Science, 131 p. John Wiley and Sons, Inc. Hoboken, New Jersey, U.S.A.
  5. ^ McKie, D., McKie, C. (1986) Essentials of Crystallography. III. Blackwell Scientific Publishers, p.69

External links[edit]

  • Media related to Zaïrite at Wikimedia Commons