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Rare zinc arsenate mineral From Wikipedia, the free encyclopedia
Warikahnite is a rare zinc arsenate mineral of the triclinic crystal system with Hermann-Mauguin notation 1, belonging to the space group P1.[6] It occurs in the Tsumeb mine in Namibia on corroded tennantite in the second oxidation zone under hydrothermal conditions in a dolomite-hosted polymetallic ore deposit.[5][7] It is associated with adamite, stranskiite, koritnigite, claudetite, tsumcorite, and ludlockite. The origin of discovery was in a dolomite ore formation within an oxidized hydrothermal zone, in the E9 pillar, 31st level of the Tsumeb Mine in Namibia, Southwest Africa.[2][5] It has also been found at Lavrion, Greece and Plaka, Greece as microscopic white needles.[6]
| Warikahnite | |
|---|---|
Warikahnite, Tsumeb mine, Namibia, 0.6 × 0.4 × 0.1 cm | |
| General | |
| Category | Arsenate minerals |
| Formula (repeating unit) | Zn3(AsO4)2·2H2O |
| IMA symbol | War[1] |
| Strunz classification | 8.CA.35 |
| Crystal system | Triclinic |
| Crystal class | Pinacoidal (1) (same H-M symbol) |
| Space group | P1 |
| 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 |
| Color | Pale yellow to colorless; honey-yellow; orange |
| Crystal habit | Acicular; radial |
| 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 | [2][3][4][5] |
Warikahnite was discovered by Clive Queit[6] at Tsumeb mine and was first described in 1979 by Keller, Hess, and Dunn.[2][5] The name "warikahnite" honors Walter Richard Kahn, who was born in 1911. He was from Bad 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.[2] The type material is located at the University of Stuttgart, the Smithsonian Institution, and Harvard University.[5][6]
Warikahnite has perfect cleavage on the c-axis {001}; and good cleavage on both the a- and b-axes ({100} and {010}).[5] It has bladed subhedral crystals up to 3 × .5 × .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.[6] This triclinic 1 specimen classified under the space group P1 features striated crystals up to two centimetres in radial to subparallel aggregates.[7] 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.[6]
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.[8] The "Die Kristallstruktur von Warikahnit" article also notes 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).[9]
Warikahnite has the chemical formula Zn3(AsO4)2·2H2O. Along with arsenate ions (AsO4)3−, the infrared spectrum revealed H2O.[5] 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.[10] After a microprobe analysis, the weight percent oxides were calculated as follows in the table directly below.[5]
| 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% |
Warikahnite's only known localities to date are the Tsumeb Mine in Namibia, South West Africa; and Plaka and Lavrion, Greece.[6] 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.[6]
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