Gaudefroyit

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Gaudefroyit
Gaudefroyite-Andradite-120658.jpg
Gaudefroyite (black) and andradite (red) from the Wessels Mine, Hotazel , Kalahari manganese fields, North Cape, South Africa (size: 6.8 cm × 5.7 cm × 3.2 cm)
General and classification
other names

IMA 1964-006

chemical formula Ca 4 Mn 3+ 3 [O 3 | CO 3 | (BO 3 ) 3 ]
Mineral class
(and possibly department) 		Borates (formerly carbonates, nitrates and borates)
System no. to Strunz
and to Dana 		6.AB.60 ( 8th edition : V / G.04)
01/27/02/01
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol hexagonal-pyramidal; 6th
Space group P 6 3 (No. 173)Template: room group / 173
Lattice parameters a  = 10.59  Å ; c  = 5.89 Å
Formula units Z  = 2
Frequent crystal faces {11 2 0}, {01 1 0}
Physical Properties
Mohs hardness 6th
Density (g / cm 3 ) measured: 3.35 to 3.50; calculated: 3.44 to 3.53
Cleavage is missing
Break ; Tenacity clamshell; brittle
colour copper-brown to black with strong yellow-orange to reddish internal reflections
Line color brownish gray
transparency opaque
shine Glass gloss, matt
Crystal optics
Refractive indices n ω  = 1.805 to 1.810
n ε  = 2.015 to 2.020
Birefringence δ = 0.210
Optical character uniaxial positive
Pleochroism Strong: ω = light yellowish brown; ε = red-orange

Gaudefroyite is a very rare mineral from the mineral class of "borates" (formerly carbonates, nitrates and borates) with the chemical composition Ca 4 Mn 3+ 3 [O 3 | CO 3 | (BO 3 ) 3 ] and is therefore a calcium - manganese - borate with additional oxygen - and carbonate ions .

Gaudefroyite crystallizes in the hexagonal crystal system and is found in the form of prismatic crystals with pyramidal end faces of up to 5 cm in length. Most of these are connected to form mineral aggregates that diverge in a radiant manner. The opaque crystals are from copper-brown to black in color with strong yellow-orange to reddish, inner reflections and show a glass-like sheen on the surface .

Etymology and history

Drawing of a Gaudefroyite crystal from Tachgagalt in Morocco

Gaudefroyite was first discovered by MP Gallo, who in 1962 collected mineral samples on the spoil heaps of the “Tachgagalt” manganese open-cast mine in the Moroccan province of Ouarzazate . Georges Jouravsky (1896–1964) and François Permingeate analyzed the material and were able to identify the previously unknown mineral. They named it after the French mineralogist Abbé Christophe Gaudefroy (1888–1971), who among other things worked in "Tachgagalt".

Type material of the mineral is kept in the Geological Office of Morocco in Rabat , in the Muséum national d'histoire naturelle (Catalog No. 165.34) and in the Mines ParisTech (also École des mines de Paris , English National School of Mines ) in Paris .

classification

In the outdated but still partially in use 8th edition of the mineral classification by Strunz of Gaudefroyit belonged to common mineral class of "carbonates, nitrates and borates" and then to the Department of "Island borates" where he along with Azoproit , Blatterit , Bonaccordit , Chestermanit , Fredrikssonite , Ludwigite , Orthopinakiolite , Takéuchiit and Vonsenit the "Ludwigite group" with the system no. V / G.04 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), assigns Gaudefroyite to the now independent class of "borates" and there in the department of "monoborates". This is further subdivided according to the possible presence of additional anions and the structure of the borate complexes, so that the mineral is classified according to its composition and structure in the subsection “BO 3 with additional anions; 1 (Δ) + OH etc. ”(here: a trigonal borate complex and additional oxygen and carbonate ions) can be found, where it is the only member that forms the unnamed group 6.AB.60 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Gaudefroyit to the common class of "carbonates, nitrates and borates" and there in the department of "borates", like the outdated Strunzian system. Here he is to be found as the only member of the unnamed group 01/27/02 within the subdivision “ Compound Borates ”.

Crystal structure

Gaudefroyite crystallizes hexagonally in the space group P 6 3 (space group no. 173) with the lattice parameters a  = 10.59  Å and c  = 5.89 Å as well as two formula units per unit cell . Template: room group / 173

Education and Locations

Ettringite (yellow), calcite (white), Gaudefroyite (black) and hematite (silvery single crystal) from the N'Chwaning II mine, Kuruman, Kalahari manganese ore fields, North Cape, South Africa (size: 10 cm × 8 cm × 4 cm)

Gaudefroyite is formed by hydrothermal processes in manganese deposits . At its type locality in the “Tachgagalt” manganese open-cast mine, the largest Gaudefroyite crystals with up to 5 cm prisms were discovered to date. Braunite , brucite , calcite , crednerite , hausmannite , morocite , pyrolusite and quartz appeared as accompanying minerals .

In Germany, the mineral is so far only known from the "Caspar" quarry on Ettringer Bellerberg in the Rhineland-Palatinate district of Mayen-Koblenz.

Other previously known localities are found only in the Kalahari - Manganerzfeldern the South African Northern Cape as the N'Chwaning mines at Kuruman , where as Begleitminerale still barite , Bixbyite , hematite , hydrogrossular and manganite occurred, and the Black Rock mine and Wessels Mine at Hotazel .

See also

literature

  • G. Jouravsky, F. Permingeat: La gaudefroyite, une nouvelle espèce minérale. In: Bulletin de la Société Française de Minéralogie et de Cristallographie. Volume 87 (1964), pp. 216–229 ( PDF 1 MB )
  • Michael Fleischer : New mineral names. Gaudefroyit In: American Mineralogist Volume 50 (1965), pp. 805–813 ( PDF 531.9 kB ; from p. 2)
  • C. Hoffmann, T. Armbruster, M. Kunz: Structure refinement of (001) disordered gaudefroyite Ca 4 Mn 3+ 3 [(BO 3 ) 3 (CO 3 ) O 3 ]: Jahn-Teller distortion in edge-sharing chains of Mn 3+ O 6 octahedra. In: European Journal of Mineralogy Volume 9 (1997), pp. 7-19

Web links

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

Individual evidence

  1. ↑ a b c d 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.  334 .
  2. ↑ Webmineral - Gaudefroyite
  3. ↑ a b c d e f g h Gaudefroyite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 65 , 64 kB )
  4. ↑ a b 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. ↑ a b Mindat - Gaudefroyite
  6. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  586 (first edition: 1891).
  7. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Dörfler Verlag GmbH, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 131 .
  8. ↑ Find location list for Gaudefroyit at the Mineralienatlas and at Mindat