Zaïrite

(repeating unit)Bi(Fe3+,Al)3[(OH)6|(PO4)2]IMA symbolZaï[1]Strunz classification8.BL.13Crystal systemTrigonalCrystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)Space groupR3mUnit cella = 7.015, c = 16.365 [Å]; Z = 3IdentificationFormula mass646.86 g/molColorGreenish, greenish white, yellow green.CleavageNone observedFractureIrregular, unevenTenacityBrittleMohs scale hardness4.5LusterVitreous, resinousStreakWhiteDiaphaneityTransparent to translucentSpecific gravity4.37Optical propertiesUniaxial(-)Refractive indexnω = 1.820 - 1.830 nε = 1.810Birefringenceδ = 0.0100-0.0200Other characteristicsOccurrence: Rare mineral in the weathering zone of quartz wolframite depositsReferences[2][3][4]

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

Properties

Zaïrite crystallizes in the trigonal crystal system, which means it contains three equal horizontal axes with angles of 120° between them.[5] The mineral has a trigonal-hexagonal scalenohedron shape.[6] 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.[5]

Occurrence

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.[4] 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.[2]

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. ^ a b c Mindat.org
  3. ^ a b Webmineral data
  4. ^ a b Handbook of Mineralogy
  5. ^ 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.
  6. ^ McKie, D., McKie, C. (1986) Essentials of Crystallography. III. Blackwell Scientific Publishers, p.69
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