Biehlite

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Biehlite
Biehlite.jpg
Biehlite crystals from the Tsumeb Mine in Namibia
General and classification
other names
  • GS 10
  • IMA 1999-019a
chemical formula
  • (Sb, As) MoO 6
  • (Sb 3+ , As 3+ ) 2 MoO 6
  • Sb 3+ 2 MoO 6
  • ((Sb, As) O) 2 [MoO 4 ]
Mineral class
(and possibly department)
Oxides and hydroxides
System no. to Strunz
and to Dana
4.DB.60 ( 8th edition : VI / G.02)
11.11.02.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = 18.076  Å ; b  = 5.920 Å; c  = 5.083 Å
β  = 96.97 °
Formula units Z  = 4
Physical Properties
Mohs hardness "Soft", 1–1.5
Density (g / cm 3 ) 5.23 (calculated)
Cleavage not specified
Break ; Tenacity not specified; inelastic (mildly) flexible
colour White
Line color White
transparency translucent
shine Silky gloss
Crystal optics
Refractive index n  = 2.13
Optical character biaxial (optical orientation unknown)
Other properties
Chemical behavior Biehlit is insoluble in dilute HCl, but is dissolved in concentrated HCl within seconds without leaving any residue
Special features When subjected to mechanical stress in a mortar, it disintegrates into a greenish mica-like powder

Biehlite is a very rarely occurring mineral from the mineral class of "oxides and hydroxides" (including V [5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates). It crystallizes in a monoclinic crystal system with the chemical formula (Sb, As) MoO 6 , so it is chemically an antimony - arsenic - molybdenum oxide.

Biehlite forms irregular aggregates from fibrous to thin-needle crystals up to 1 mm in length, but only a few micrometers in diameter, as well as felt-like masses. The mineral was found - together with large angelsite - and small brown wulfenite crystals - in a fine-grained dark copper ore in the Tsumeb Mine, Namibia.

Etymology and history

The discoverer of the biehlite is an unknown miner who was probably able to recover steps of the new mineral on the third oxidation zone of the Tsumeb Mine . Material with biehlite crystals first appeared on the market in 1989 and was probably found that year as well. Although it quickly became clear that this was a new mineral, the identification process turned out to be very tedious, which was mainly due to the fibrous nature of the crystals. Only after further extensive investigations were the data required by the International Mineralogical Association (IMA) completed, so that the mineral was recognized by the IMA on December 2, 1999 under the number IMA 1999-019a. In 2000 it was described as Biehlite by a German research team with Jochen Schlueter, Karl-Heinz Klaska, Gunadi Adiwidjaja, Karen Friese and Georg Gebhard in the German science magazine “New Yearbook for Mineralogy, Monthly Issues”.

The mineral was named after the Münster mineralogist Friedrich Karl Biehl (1887–?), Who was one of the first mineralogists to deal in detail with the minerals of Tsumeb and in 1919 with a thesis on "Contributions to the knowledge of the minerals in the ore deposits of Tsumeb" received his doctorate.

The type material acquired by Jochen Schlüter at the Munich Mineral Fair in October 1991 from Clive Queit , Johannesburg, is kept at the University of Hamburg in Germany (holotype, collection no. MMHH TS 220, in the museum's safe).

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the biehlite belonged to the mineral class of " sulfates , chromates , molybdates and tungstates (as well as some selenates and tellurates)" and there to the department of "molybdates and tungstates", where he together with Cuprotungstit , Ferrimolybdit , Lindgrenit , Szenicsit and Vergasovait the "Lindgrenit-Ferrimolybdit-Gruppe" with the system no. VI / G.02 formed.

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 biehlite to the class of “oxides and hydroxides” and there to the department of oxides with the substance ratio “metal: oxygen = 1: 2 and comparable “. This section is further subdivided according to the relative size of the cations involved and the crystal structure , so that the mineral is classified according to its composition in the sub-section “With medium-sized cations; Chains of Edge-Linked Octahedra ”can be found, where it is the only member of the unnamed group 4.DB.60 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns biehlite to the class of "phosphates, arsenates and vanadates", but also to the category of "molybdates and tungstates" there. Here he is the only member of the unnamed group 48.02.04 within the sub-section “ Anhydrous molybdates and tungstates with (A) 2 XO 4 ”.

Chemism

Average values from five microprobe analyzes on Biehlite from Tsumeb led to contents of 33.76% MoO 3 , 60.99% Sb 2 O 3 and 4.95% As 2 O 3 . This resulted in the empirical formula (Sb 3+ 1.79 As 3+ 0.21 ) Σ = 2.00 Mo 6+ 1.00 O 6 (Sb, As) 2 (based on six anions ) MoO 6 has been simplified. The ideal chemical formula Sb 2 MoO 6 requires 66.94% Sb 2 O 3 and 33.06% MoO 3 . Further chemical analyzes ( neutron activation analysis , ICP-AES ) provide different results with significantly lower values ​​for MoO 3 , Sb 2 O 3 and As 2 O 3 , for which no explanation was found.

Crystal structure

Biehlite crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 18.076  Å ; b  = 5.920 Å; c  = 5.083 Å and β = 96.97 ° as well as four formula units per unit cell . Template: room group / 15

The structure of the biehlite is a typical chain structure in which the bonds within the chains are considerably stronger than those connecting adjacent chains. The Mo 6+ ion is coordinated by the oxygen atoms in such a way that a strongly distorted octahedron is formed. These octahedra have common edges, creating zigzag chains with the composition [Mo 2 O 8 ] 4− , which run parallel to the crystallographic c-axis [001]. Each antimony ion forms a short bond with the oxygen O2 of the octahedron and also has two short bonds with the oxygen O1. In this way, the [Mo 2 O 8 ] 4− chain of octahedra is flanked on each side by [Sb 2 O 2 ] 2+ groups, creating infinite bands of the composition [Sb 4 Mo 2 O 12 ], which in Direction [001]. Adjacent bands are only held together by weak Sb-O bonds in directions [100] and [010], which is also the reason for the asbestos-like splintering of the biehlite fibers. In contrast to almost all structures of chemically similar compounds, biehlite is not a structure made up of intimately connected layers, but a one-dimensional chain structure.

Stibivanite has structural similarities and similarities with biehlite. The structure of synthetic Sb 2 MoO 6 is closely related to that of the “Aurivillius phases” with the composition ( Bi 2 O 2 ) (A n −1 M n X 3 n +1 ). Some are selective catalysts for the oxidation of alkenes and have interesting physical properties such as ferroelectricity , piezoelectricity , pyroelectricity and nonlinear dielectric susceptibility .

properties

morphology

Biehlite forms fibrous to thin-needle crystals, stretched along the c-axis [001], up to 1 mm in length, but only a few micrometers in diameter, which come together to form irregular, confused, nested or felt-like aggregates.

physical and chemical properties

Biehlite crystals are white, their line color is also white. The surfaces of the translucent crystals show a distinct silky sheen .

No cleavage was found on the crystals of the biehlite . The mineral is described as "soft" and has a Mohs hardness of 1 to 1.5. As with asbestos minerals , the thin crystals are inelastic, flexible and split into ever thinner fibers when subjected to mechanical stress. When subjected to mechanical stress in a mortar , Biehlite disintegrates into a greenish, mica-like powder, which still shows the same peaks in the X-ray diffraction , but with lower intensities. Measured values ​​for the density of the biehlite do not exist, the calculated density for the mineral is 5.23 g / cm³.

Biehlite is insoluble in dilute hydrochloric acid (HCl), but is dissolved in concentrated HCl within seconds, this solution leaving a blue residue on evaporation.

Education and Locations

Biehlit arises as a typical secondary education in a complex, sitting in carbonate rocks Cu-Pb-Zn ore - deposit . Antimony, arsenic and molybdenum come from the decomposition of former sulphidic ore minerals. Biehlite occurs together with large, colorless angelsite crystals and small brown wulfenite crystals on a matrix of a fine-grained dark copper ore.

As a very rare mineral formation, Biehlite could only be described from one source so far (as of 2016). Its type locality is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto Region , Namibia . The exact location within the Tsumeb Mine is unknown, but should be within the third oxidation zone , which begins at a depth of 1,350 meters and extends over the area between levels 42 to 48.

use

Due to its rarity, biehlite is only of interest to mineral collectors.

See also

literature

  • Biehlite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 64 kB ; accessed on August 27, 2019]).
  • Gunadi Adiwidjaja, Karen Friese, Karl-Heinz Klaska, Jochen Schlüter, M. Czank: Crystal structure and crystal chemistry of biehlite, Sb 1.79 As 0.21 MoO 6 . In: Journal of Crystallography . tape 215 , 2000, pp. 529–535 , doi : 10.1524 / zkri.2000.215.9.529 ( rruff.info [PDF; 909 kB ]).

Web links

Commons : Biehlite  - collection of images, videos and audio files

Individual evidence

  1. a b c d e f g h i j k l m n o p q Jochen Schlüter, Karl-Heinz Klaska, Gunadi Adiwidjaja, Karen Friese and Georg Gebhard: Biehlite, (Sb, As) 2 MoO 6 , a new mineral from Tsumeb, Namibia . In: New yearbook for mineralogy, monthly books . tape 2000 , 2000, pp. 234-240 .
  2. a b Biehlite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 64  kB ; accessed on August 27, 2019]).
  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.  728 (English).
  4. a b Biehlite. In: mindat.org. Hudson Institute of Mineralogy, accessed August 27, 2019 .
  5. Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Reichshof 1991, p. 226 .
  6. Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, p. 294, 320 .
  7. ^ Friedrich Karl Biehl: Contributions to the knowledge of the minerals of the ore deposits of Tsumeb [Inaugural dissertation to obtain the doctorate of the Philosophical and Natural Science Faculty of the Westphalian Wilhelms University in Münster (Westphalia)] . 1st edition. Carl Biehl, Osnabrück 1919, p. 1-59 .
  8. ↑ Type mineral catalog Germany - storage of the holotype stage Biehlite. In: typmineral.uni-hamburg.de. University of Hamburg , accessed on August 27, 2019 .
  9. Catalog of Type Mineral Specimens - https://docs.wixstatic.com/ugd/839128_f154afcb791940f7a8ef961500180d63.pdf. (PDF 80 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 27, 2019 .
  10. a b Gunadi Adiwidjaja, Karen Friese, Karl-Heinz Klaska, Jochen Schlüter, M. Czank: Crystal structure and crystal chemistry of biehlite, Sb 1.79 Ace 0:21 MoO 6 . In: Journal of Crystallography . tape 215 , 2000, pp. 529–535 , doi : 10.1524 / zkri.2000.215.9.529 ( rruff.info [PDF; 909 kB ]).
  11. Localities for Biehlite. In: mindat.org. Hudson Institute of Mineralogy, accessed August 27, 2019 .
  12. a b List of locations for Biehlite in the Mineralienatlas and Mindat