Kombatit

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Kombatit
Kombatite.jpg
Yellow Kombatite crystals on matrix from the type locality Kombat Mine, Grootfontein , Namibia
General and classification
other names

IMA 1985-056

chemical formula
  • Pb 14 [Cl 4 | O 9 | (VO 4 ) 2 ]
  • Pb 14 O 9 (VO 4 ) 2 Cl 4
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.BO.20 ( 8th edition : III / D.10)
41.01.04.02
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  = 12.68  Å ; b  = 22.57 Å; c  = 11.28 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 2 to 3
Density (g / cm 3 ) measured: 4.3; calculated: 7.979
Cleavage completely after {010}
Break ; Tenacity brittle
colour light yellow
Line color pale yellow
transparency translucent
shine Diamond luster
Crystal optics
Refractive index n  > 1.90
Optical character biaxial negative

Kombatit is a very rarely occurring mineral from the mineral class of "phosphates, arsenates and vanadates" with the chemical composition Pb 14 [Cl 4 | O 9 | (VO 4 ) 2 ] and is therefore chemically a lead - vanadate with additional chlorine - and oxygen - ions and the vanadium analogue of Sahlinit .

Kombatite crystallizes in the monoclinic crystal system , but has so far only been found in the form of irregular, cloudy grains up to about 0.2 mm in size. The mineral is translucent and shows a diamond-like sheen on the surfaces of the light yellow grains . Its line color is also pale or light yellow.

Etymology and history

Kombatit was first discovered in the copper mine of the same name near the private settlement of Kombat in the Namibian region of Otjozondjupa . The mineral was first described in 1986 by RC Rouse, Pete J. Dunn and J. Innes, who named it after its type locality .

The type material of the mineral is listed in the Geological Survey of Canada in Ottawa (Canada) under catalog no. 64563 kept.

classification

In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the kombatite still belonged to the mineral class of "halides" and there to the department of "oxyhalides", where it together with asisite , blixite , chubutite (rejected by the IMA), Damarait , Ekdemit , Heliophyllit , Mendipite , Mereheadit , Nadorit , Parkinsonit , Penfieldit , Perit , Philolithit , Pinalit , Sahlinit , Schwartzembergit , Seeligerit , Sundiusit , Symesit and Thorikosit the "Mendipite-Nadorit group" with the system number. III / D.10 .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns kombatite to the class of “phosphates, arsenates and vanadates” and there in the department of “phosphates, etc.” further anions , without H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the additional anions (OH, etc.) to the phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral according to its composition in the subsection “With exclusively large cations; (OH, etc.): RO 4  ≥ 1: 1 "can be found, where the" Sahlinite group "with the system no. 8.BO.20 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the kombatite to the class of "phosphates, arsenates and vanadates" and there to the category of "anhydrous phosphates, etc., with hydroxyl or halogen". Here he is also together with Sahlinit in the unnamed group 41.01.04 within the subdivision “Anhydrous phosphates etc., with hydroxyl or halogen with (A 2+ ) m (XO 4 ) p Z q , with m: p> 4: 1 " to find.

Chemism

The analysis with the aid of the electron microprobe showed an average composition of 92.4% PbO , 5.9% V 2 O 5 , 4.2% chlorine (Cl) and 0.9% O = Cl (Σ = 101.6 wt. %), which corresponds to the empirical formula Pb 13.7 V 2.1 O 17.1 Cl 3.9 for (O, Cl) = 21.

The result of the analysis comes very close to the idealized chemical composition Pb 14 [Cl 4 | O 9 | (VO 4 ) 2 ], which is 84.91% lead, 4.15% chlorine, 2.98% vanadium and 7.96 % Oxygen.

Crystal structure

Kombatite crystallizes isostructurally (in the same structure type ) with sahlinite in the monoclinic crystal system in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 12.68  Å ; b  = 22.57 Å; c  = 11.28 Å and β = 118.1 ° as well as 4 formula units per unit cell . Template: room group / 15

The crystal structure of Kombatit consists of double layers parallel to the b-surface (010) or at right angles to the y-axis. Two layers of PB (O, Cl) 5-8 - polyhedra are linked with VO 4 - tetrahedra and connected to the neighboring double layers by a layer of Cl atoms.

Education and Locations

Kombatit formed in layered manganese - ore . As Begleitminerale occur among other calcite , hematite , Hausmannite and Kentrolith , one the Harkerit like mineral on.

Apart from its type locality, the Kombat Mine in Namibia, the mineral is known so far (as of 2018) only from the Wesley Mine near Westbury on Trym just 5 km north of Bristol in England .

use

Due to its extreme rarity, Kombatit is only of interest to collectors.

See also

literature

  • RC Rouse, Pete J. Dunn, J. Innes: Kombatite, the vanadium analogue of sahlinite, from the Kombat mine, South West Africa . In: New yearbook for mineralogy, monthly books . 1986, p. 519-522 .
  • John Leslie Jambor , Kenneth W. Bladh, T. Scott Ercit, Joel D. Grice, Edward S. Grew: New mineral names . In: American Mineralogist . tape 73 , 1988, pp. 927-935 ( rruff.info [PDF; 879 kB ; accessed on June 6, 2018]).
  • Mark Cooper, Frank C. Hawthorne: The crystal structure of kombatite, Pb 14 (VO 4 ) 2 O 9 Cl 4 . In: American Mineralogist . tape 79 , 1994, pp. 550–554 ( minsocam.org [PDF; 529 kB ; accessed on June 6, 2018]).
  • Pete J. Dunn: Rare minerals of the Kombat mine . In: The Mineralogical Record . tape 22 , no. 6 , 1991, pp. 421-425 .
  • Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason , Abraham Rosenzweig: Dana's New Mineralogy . 8th edition. John Wiley & Sons, New York (et al.) 1997, ISBN 0-471-19310-0 , pp. 817 .

Web links

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

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names; March 2018 (PDF 1.65 MB; Kombatit see p. 100)
  2. ↑ a b c d e 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.  469 .
  3. ↑ a b c d e f Kombatite . 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; 64  kB ; accessed on June 5, 2018]).
  4. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  5. ↑ John Leslie Jambor , Kenneth W. Bladh, T. Scott Ercit, Joel D. Grice, Edward S. Grew: New mineral names . In: American Mineralogist . tape  73 , 1988, pp. 927-935 ( rruff.info [PDF; 879 kB ; accessed on June 6, 2018]).
  6. ↑ Webmineral - Kombatite (English)
  7. ↑ Find location list for Kombatit in the Mineralienatlas and Mindat