Warikahnite

Warikahnite

Warikahnite, Tsumeb mine, Namibia, 0.6 x 0.4 x 0.1 cm
General
Category Arsenate minerals
Formula
(repeating unit)		 Zn3(AsO4)2•2H2O
Strunz classification 8.CA.35
Crystal system Triclinic
Unit cell a = 6.71 Å, b = 8.98 Å
c = 14.53 Å; α = 105.59°
β = 93.44°, γ = 108.68°; Z = 4
Identification
Formula mass 510.04 g mol−1
Color Pale yellow to colorless; honey-yellow; orange
Crystal habit Acicular; radial
Crystal symmetry Triclinic - pinacoidal
H-M symbol: (1)
Space group: P1
Cleavage [001] perfect, [010] good, [100] good
Fracture Brittle
Mohs scale hardness 2
Luster Vitreous, waxy
Streak White
Diaphaneity Transparent
Specific gravity 4.28
Optical properties Biaxial (+)
Refractive index nα = 1.747 nβ = 1.753 nγ = 1.768
Birefringence δ = 0.021
2V angle 75° measured
References [1][2][3][4]

Warikahnite is a rare zinc arsenate mineral of the triclinic crystal system with Hermann- Mauguin notation 1, belonging to the space group P1.[5] It occurs in the Tsumeb mine in Namibia on corroded tennantite in the second oxidation zone under hydrothermal conditions in a dolostone-hosted polymetallic ore deposit.[4][6] It is associated with adamite, stranskiite, koritnigite, claudetite, tsumcorite, and ludlockite. The origin of discovery was in a dolostone ore formation within an oxidized hydrothermal zone, in the E9 pillar, 31st level of the Tsumeb Mine in Namibia, Southwest Africa.[1][4] It has also been found at Lavrion, Greece and Plaka, Greece as microscopic white needles.[5]

Discovery

Warikahnite, Tsumeb mine, Namibia, 0.9 x 0.4 x 0.1 cm

Warikahnite was discovered by Clive Queit[5] at Tsumeb mine and was first described in 1979 by Keller, Hess, and Dunn.[1][4] The name "warikahnite" honors Walter Richard Kahn, who was born in 1911. He was from Bayersoien, Germany, and he was a dealer and collector that specialized in Tsumeb minerals. He was honored due to his support of research into rare secondary minerals.[1] The type material is located at the University of Stuttgart, the Smithsonian Institution, and Harvard University.[4][5]

Physical properties

Warikahnite has perfect cleavage on the c-axis {001}; and good cleavage on both the a- and b-axes ({100} and {010}).[4] It has bladed subhedral crystals up to 3 x .5 x .5 mm, elongated on {100} and flattened on {010}, with a hardness of approximately 2 as presented in table two. Its specific gravity is 4.24 and it exhibits a colorless to pale yellow hue, along with a white streak and vitreous luster.[5] This triclinic 1 specimen classified under the space group P1 features striated crystals up to two centimetres in radial to subparallel aggregates.[6] The Handbook of Mineralogy further states the cell dimensions of biaxial Warikahnite to be calculated as a = 6.710(1) Å, b = 8.989(2) Å, and c = 14.533(2) Å, with unit cell volume as 788.58 Å.[5]

Crystal structure

Structure

The crystal structure of Warikahnite, determined from diffractometer data, contained six various coordination polyhedra of zinc with components of As, O, and H₂O; with the coordination numbers six, five, and four; and with five different combinations of ligand.[7] Also noted in the “Die Kristallstruktur von Warikahnit” article, is that the hydrogen bonds are discussed appertaining to both charge balance and infrared spectra. Recent data shows the Gladstone-Dale relation compatibility of Warikahnite is ranked as superior (-0.010).[8]

Chemical composition

Warikahnite has the chemical formula Zn3(AsO4)2•2H2O. Along with arsenate ions (AsO₄)3−, the infrared spectrum revealed H₂O .[4] These water molecules present in the warikahnite sample were determined by thermo gravimetric analysis, and lost at 365°C. Both H₂O and (AsO₄)3− readily dissolved when hot hydrochloric acid (HCL) or nitric acid (HNO₃) were added to the specimen.[9] After a microprobe analysis, the weight percent oxides were calculated as follows in the table directly below.[4]

Chem For. Name %
As₂O₅ (arsenic pentoxide) 44.33%
ZnO (zinc oxide) 47.85%
MnO (manganese oxide) 0.40%
FeO (iron oxide) 0.19%
H₂O (water) 6.32%
TOTAL 99.09%

Geologic occurrence

Warikahnite’s only known localities to date are the Tsumeb Mine in Namibia, South West Africa; and Plaka and Lavrion, Greece.[5] The first discovery of this type specimen in the mine was found with white koritnigite, blue stranskiite, pale to emerald-green cuprian adamite, crystals of helmutwinklerite, and white corroded crystals of claudetite, ludlockite, tsumcorite, and lavendulan; while the second acquisition was only linked to quartz.[5]

See also

References

  1. 1 2 3 4 http://rruff.geo.arizona.edu/doclib/hom/warikahnite.pdf Mineral Handbook
  2. ↑ http://webmineral.com/data/Warikahnite.shtml Webmineral
  3. ↑ http://www.mindat.org/min-4244.html Mindat
  4. 1 2 3 4 5 6 7 8 Fleischer, Michael; L. J. Cabri; A. Pabst (1980). "New mineral names" (PDF). American Mineralogist 65: 406–408. Retrieved 2010-01-03.
  5. 1 2 3 4 5 6 7 8 Pinch, William W. (July 2005). "Warikahnite: some background on the cover specimen.". The Mineralogical Record (The Mineralogical, Inc.) 36 (4): 315(1).
  6. 1 2 Anthony, J. W., Bideaux, R. A., Bladh, K. W., and Nichols, M. C. (2000) Handbook of Mineralogy. Volume IV: Arsenates, Phosphates and Vanadates. Mineral Data Publishing Company, Tucson, Arizons, p. 644
  7. ↑ Riffel, H., P. Keller, and H. Hess (1980) Die Kristallstruktur von Warikahnit, Zn₃(AsO₄)₂•2H₂O Tschermaks Mineral. Petrog. Mitt., 27, 187–199 (in German with English abs)
  8. ↑ Mandarino, Joseph A. (2006). "The Gladstone-Dale Compatibility of Arsenate Minerals". Periodico di Mineralogia 75 (2-3): 167–174.
  9. ↑ Keller, P., Hess, H., and Dunn, P.J. (1979) Warikahnit, ein neues Mineral aus Tsumeb, Sudwestafrika. Neues Jahrbuch fur mineralogy, Monatshefte, 389-395. Abstracted in American Mineralogist, 65, 408
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Literature

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