Braunite

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Braunite
Braunite-195641.jpg
Braunite crystal specimen from the Wessels Mine, Hotazel, Kalahari Manganfeld, North Cape, South Africa (size 2.9 cm × 2.1 cm × 1.8 cm)
General and classification
chemical formula Mn 2+ Mn 3+ 6 [O 8 | SiO 4 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.AG.05 ( 8th edition : VIII / B.09)
07.05.01.01 (Braunite-I)
Similar minerals Hausmannite , magnetite
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol ditetragonal-dipyramidal; 4 / m  2 / m  2 / m
Space group I 4 1 / acd (No. 142)Template: room group / 142
Lattice parameters a  = 9.41  Å ; c  = 18.67 Å
Formula units Z  = 8
Twinning according to (111) or {112}
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 4.72 to 4.83; calculated: [4.86]
Cleavage completely after {112}
Break ; Tenacity uneven to slightly scalloped
colour iron to brownish black
Line color brownish black to black
transparency opaque (opaque)
shine Metallic luster
magnetism weakly magnetic
Other properties
Chemical behavior Slightly soluble in HCl , is decomposed by HNO 3

Braunite (also hard brown stone , heteroclase , heterocline or pesillite ) is a rather seldom occurring mineral from the mineral class of " silicates and germanates " with the chemical composition Mn 2+ Mn 3+ 6 [O 8 | SiO 4 ] and is therefore a chemical one manganese silicate with additional oxygen - ions .

Braunite crystallizes in the tetragonal crystal system , but develops only small, pyramidal and octahedral, {001} and {201} striped crystals up to about 5 cm in size. It is mostly found in the form of crust-shaped crystal turf or granular to massive mineral aggregates . The mineral is opaque, but not completely opaque , and shows a faint to greasy metallic sheen on the surfaces of the iron- to brownish-black crystals . Braunite leaves a black, finely rubbed, somewhat brownish line on the marking board .

Braunite forms a complete mixed series with Abswurmbachit .

Etymology and history

Braunite was first found in the Oehrenstock quarry near Langewiesen in the Thuringian Forest and was described in 1826 by Wilhelm Ritter von Haidinger , who named the mineral after him in honor of the Chamber Councilor Wilhelm von Braun zu Gotha.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the brownite belonged to the mineral class of "silicates and germanates" and there to the department of "island silicates with non-tetrahedral anions (Neso-subsilicates)", where it was named after Långbanit the "Braunit Långbanit Group" with the system no. VIII / B.09 and the other members Abswurmbachit , Franciscanit , Katoptrit , Neltnerit , Örebroit , Welinit , Yeatmanit and Zoltaiit .

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 classifies Braunite in the category of "island silicates (nesosilicates)". This is further subdivided according to the possible presence of additional anions and the coordination of the cations involved , so that the mineral is classified according to its composition in the sub-section “Island silicates with additional anions; Cations are mostly found in [6] er and> [6] er coordination ”, where the“ Braunite group ”with the system no. 9.AG.05 and the other members Abswurmbachit, Braunit II (N) and Neltnerite.

The systematics of minerals according to Dana , which is common in the English-speaking world , classifies Braunite (here Braunit-I ) not with silicates but with oxides. Together with neltnerite , Braunite-II and Abswurmbachit, it forms the " humite group (tetragonal: I41 / acd) with Si " within the subdivision of "multiple oxides with the general formula ABX 2 ".

Crystal structure

Braunite crystallizes tetragonally in the space group I 4 1 / acd (space group no. 142) with the lattice parameters a  = 9.41  Å and c  = 18.67 Å as well as 8 formula units per unit cell . Template: room group / 142

Modifications and varieties

Braunit-II is a calcium-containing variety.

Education and Locations

Braunite with andradite (orange) from the N'Chwaning mines, Kuruman, Kalahari manganese field, North Cape, South Africa (size 4.4 cm × 4.3 cm × 2 cm)

Braunite is formed by metamorphosis or weathering from manganese silicates and oxides . Accompanying minerals include pyrolusite , jacobsite , hausmannite , bixbyite , rhodonite , spessartine and hematite .

So far, Braunite has been found at over 300 sites (as of 2009), including in Australia , Belgium , Chile , China , Germany , France , Greece , Great Britain , India , Indonesia , Ireland , Italy , Japan , Canada , Kazakhstan , Madagascar , Morocco , Macedonia , Mexico , New Zealand , Norway , Oman , Austria , Pakistan , Poland , Portugal , Russia , Sweden , Switzerland , Slovakia , Spain , South Africa , South Korea , Czech Republic , Turkey , Ukraine and the USA .

use

Braunite is used as manganese ore when it is locally enriched.

See also

literature

  • W. Haidinger: On the crystalline forms and properties of the manganese ores . In: The Edinburgh Journal of Science . tape 4 , 1826, pp. 41–50 ( rruff.info [PDF; 799 kB ; accessed on March 10, 2018]).
  • W. Haidinger: Mineralogical description of manganese ores IV. Brachytypes Manganese ore, Braunite . In: Annals of Physics and Chemistry . tape 14 , 1828, pp. 197–211 ( rruff.info [PDF; 629 kB ; accessed on March 10, 2018]).
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 206 .

Web links

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

Individual evidence

  1. ↑ 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.  553 .
  2. ↑ a b Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p.  490-491 .
  3. ↑ a b Webmineral - Braunite-I (English)
  4. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  703-704 .
  5. ↑ a b c d e f g Braunite . 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 ]).
  6. ↑ 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 .
  7. ↑ a b c Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  510-511 (first edition: 1891).
  8. ^ A b Paul Ramdohr : The ore minerals and their adhesions . 4th, revised and expanded edition. Akademie-Verlag, Berlin 1975, p.  1017-1022 .
  9. ↑ List of localities for Braunite in the Mineralienatlas and in Mindat - Localities for Braunite (English)