Warikahnit

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Warikahnit
Warikahnite-mf19b.jpg
General and classification
other names

IMA 1978-038

chemical formula
  • Zn 3 [(H 2 O) 2 | (AsO 4 ) 2 ]
  • Zn 3 (AsO 4 ) 2 · 2H 2 O
  • Zn 2 [6] Zn [4] [AsO 4 ] 2 · 2H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.CA.35 ( 8th edition : VII / C.07)
03/40/01/01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 6.710  Å ; b  = 8.989 Å; c  = 14.533 Å
α  = 105.59 °; β  = 93.44 °; γ  = 108.68 °
Formula units Z  = 4
Frequent crystal faces {010}, {001}, {100} and {0kl} and possibly {hkl}
Physical Properties
Mohs hardness ≈ 2
Density (g / cm 3 ) ≥ 4.24 (measured); 4.29 (calculated)
Cleavage completely according to {001}, good according to {010} and {100}
Break ; Tenacity not specified; not specified
colour light yellow to colorless, yellow-orange
Line color colorless, so probably white
transparency clear as water
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.747
n β  = 1.753
n γ  = 1.768
Birefringence δ = 0.21
Optical character biaxial positive
Axis angle 2V = 75 °
Other properties
Chemical behavior soluble in hot hydrochloric acid and nitric acid

Warikahnit is a very rarely occurring minerals from the mineral class of " phosphates , arsenates , and vanadates " with the chemical composition Zn 3 (AsO 4 ) 2 · 2H 2 O and is therefore chemically seen a hydrous zinc - arsenate .

Warikahnite crystallizes in the triclinic crystal system and develops slat-shaped, sub- idiomorphic , striped crystals up to 2 cm in size, which are typically stretched along the a-axis [100] and flattened along the pinacoid {010}. They come together to form radial to sub-parallel aggregates .

Etymology and history

The South African mineral trader Clive S. Queit , who noticed the mineral among other specimens from Tsumeb in the 1970s, is considered to have discovered warikahnite . Corresponding investigations led to the determination of the presence of a new mineral, which was recognized by the International Mineralogical Association (IMA) in 1978 and described as warikahnite in 1979 by a German-American research team with Paul Keller , Heinz Hess and Pete J. Dunn . The mineral was named after the German travel entrepreneur and hobby mineralogist Walter Richard Kahn (1911–2009) in recognition of his generous support for research into the special mineralogy of secondary minerals and their crystal structures. A second Warikahnite find with much more spectacular material was made in the Tsumeb Mine in 1984 by the miner Hannes Schoombie.

Type material of the mineral is available at the University of Stuttgart (holotype, catalog number and location TM-78.38-0703.05 / 0/824-s27 / 2); at Harvard University , Cambridge , Massachusetts (catalog numbers 117116, 117117) and in the National Museum of Natural History , Washington, DC (catalog numbers 144801, 144802, 147462).

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Warikahnit belonged to the department of "water containing phosphates without foreign anions " where he along with Fervanit , Kolovratit , Schubnelit and Serrabrancait the unnamed group with the system no. VII / C.07 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns warikahnite to the category of “phosphates etc. without additional anions; with H 2 O “. This, however, is further divided according to the relative size of the participating cations , so that the mineral according to its composition in the subsection "With large and small / medium-sized cations" is to find where it is the only member of the unnamed group 8.CA.35 forms .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns warikahnite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here he is to be found as the only member of the unnamed group 40.03.01 within the subdivision of " Water-containing phosphates etc., with (A 2+ ) 3 (XO 4 ) 2 × x (H 2 O) ".

Crystal structure

Crystallographic Data
Crystal structure of warikahnite
Crystal structure of warikahnite
Crystal system triclinic
Room group (no.) P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 6.710  Å ; b  = 8.989 Å; c  = 14.533 Å;

α = 105.59 °; β = 93.44 ° γ = 108.68 °

Formula units Z  = 4

Warikahnite crystallizes in the triclinic crystal system in the space group P 1 (space group no. 2) with the lattice parameters a  = 6.710  Å ; b  = 8.989 Å; c  = 14.533 Å; α = 105.59 °; β = 93.44 ° and γ = 108.68 ° as well as four formula units per unit cell . Template: room group / 2

Despite the simple chemical formula, the crystal structure of warikahnite contains six symmetrically different coordination polyhedra of zinc (an almost regular octahedron Zn (1) (H 2 O) 2 O 4 , a strongly deformed octahedron Zn (2) O 6 , a weakly deformed octahedron Zn (3) (H 2 O) O 5 , a strongly deformed trigonal bipyramid Zn (4) (H 2 O) O 4 , a deformed trigonal bipyramid Zn (5) (H 2 O) O 4 and a deformed tetrahedron Zn (6 ) O 4 ) with five different ligand combinations and the coordination numbers 6, 5 and 4. The cation coordination polyhedra are linked to form a wide-meshed framework in which smaller groups are characterized by an edge connection.

The Zn (1) coordination polyhedra form groups of two over common edges. Two Zn (3) coordination polyhedra are linked to these groups of two via further edges. Ultimately, a stretched, edge-linked group of six is ​​created by further linking the Zn (3) with the Zn (5) coordination polyhedra. These groups of six are point-symmetrical to the center of symmetry and are not connected to any other coordination polyhedron whose cation lies within the same unit cell.

Edge-linked groups of four arise around the center of symmetry. Two Zn (4) coordination polyhedra are connected to two Zn (2) coordination polyhedra with a common edge via edges. The groups of six and four of neighboring unit cells form zigzag chains in the direction of [101] over common corners in the plane (010). The loose framework of cation coordination polyhedra is created by including the Zn (6) coordination polyhedra, which have three corners in common with the Zn (2), Zn (4) and Zn (5) coordination polyhedra. In this way, the zigzag chains are connected in the direction of the a and b axes. The four symmetrically different, partly strongly deformed AsO 4 tetrahedra stabilize the framework structure. Hydrogen bonds in the crystal structure of warikahnite not only balance the charge for the ligands, but also for the coordination polyhedra themselves.

properties

morphology

Warikahnite in the first finds from Tsumeb forms more or less clearly radial to subparallel aggregates of coarse-grained, strongly striped, xenomorphic to subidiomorphic crystals. The crystals are up to 3 × 0.5 × 0.5 mm in size, stretched along the a-axis [100] and flattened along the pinacoid {010}. The surface shapes {010}, {001}, {100} and {0 kl } and possibly { hkl } were observed on the crystals . Only when it was found in 1984 were five steps with clearly formed crystals recovered. The crystals show clear striations and reach lengths of up to 2 cm. At the best existing level, shown on the cover picture of the Mineralogical Record (Issue 4 of 2005), the warikahnite crystals have grown together to form a wheat sheaf-like aggregate 3 cm high and 1 × 1.8 cm in cross-section.

physical and chemical properties

The crystals of warikahnite are light yellow to colorless or yellow-orange. The line color of the mineral is indicated in the original publication as colorless. Since the powder color of a mineral (which corresponds to the line color) cannot be colorless, warikahnite should have a white to slightly yellowish line. The surfaces of the water-clear, transparent crystals have a glass-like sheen .

The mineral has perfect cleavage according to {001} and two good cleavages according to {010} and {100}. With a Mohs hardness of ≈ 2, warikahnite is one of the soft minerals that, like the reference mineral plaster, can be scratched with the fingernail. The calculated density of the mineral is 4.29 g / cm³.

Warikahnite dissolves in hot hydrochloric acid and nitric acid .

Education and Locations

Warikahnite from the Tsumeb Mine (size: 1.1 × 0.3 × 0.1 cm)

So far (as of 2016) the mineral could only be found at its type locality and two other sites. The type locality is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto region , Namibia . Further finds are made at “Shaft No. 132 "of the" Christiana Mine "near Agios Konstantinos (Kamariza) and in the" Plaka Mine No. 80 ”(Filoni 80) near Plaka, all in Lavrion District, Attica Region , Greece .

Warikahnite is a typical secondary mineral and formed in the oxidation zone of the hydrothermal polymetallic ore deposit Tsumeb, which is located in dolomite stones , together with other zinc- and arsenic-containing minerals.

The first fund managed on E9 Pillar on the 31st floor . Light, poisonous green, copper-containing adamin , blue stranskiite , white coritnigite , claudetite and, more rarely, yellowish green tsumcorite and brown ludlockite were identified as accompanying minerals . The second find, documented in 1984, also occurred on the 31st level, but on the "O stope". Here the mineral was accompanied exclusively by quartz . Some of the "Warikahnites" from Tsumeb (yellow prisms, associated with copper-containing adamin and olivite aggregates) that were marketed in the late 1980s and thereafter have proven to be willemite .

use

With a ZnO content of around 48%, Wahrikahnite would be a rich zinc ore. However, with around ten known levels, it is one of the rarest secondary minerals in the Tsumeb Mine and is therefore only of interest to mineral collectors.

See also

literature

  • Paul Keller, Heinz Hess, Pete J. Dunn: Warikahnit, Zn 3 (H 2 O) 2 [(AsO 4 ) 2 ], a new mineral from Tsumeb, South West Africa . In: New yearbook for mineralogy, monthly books . tape 9 , 1979, pp. 389-395 .
  • Warikahnit. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001. ( PDF; 66 kB )

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s t u Paul Keller, Heinz Hess, Pete J. Dunn: Warikahnit, Zn 3 (H 2 O) 2 [(AsO 4 ) 2 ] , a new mineral from Tsumeb, South West Africa . In: New yearbook for mineralogy, monthly books . tape 1979 , issue 9, 1979, p. 389-395 .
  2. ↑ a b IMA / CNMNC List of Mineral Names; July 2017 (PDF 1.66 MB)
  3. ^ Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  473 .
  4. ↑ a b c d e f Warikahnite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 66  kB ; accessed on September 25, 2017]).
  5. ↑ a b c d e William W. Pinch: Warikahnit: Some background on the cover specimen . In: Mineralogical Record . tape 36 , no. 4 , 2005, p. 315 .
  6. ^ Type mineral catalog Germany - storage of the holotype stage Warikahnit
  7. ↑ H. Riffel, Paul Keller, Heinz Hess: The crystal structure of Warikahnit, Zn 3 [(H 2 O) 2 | (AsO 4 ) 2 ] . In: Tschermaks mineralogical and petrographic communications . tape 27 , 1980, pp. 187-632 .
  8. ↑ Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, p. 255 .
  9. ↑ Mindat - Number of localities for Wahrikahnit
  10. ↑ List of localities for warikahnite in the Mineralienatlas and Mindat
  11. ↑ Mindat - Warikahnit