Storm manite
| Storm manite | |
|---|---|
 |
|
| General and classification | |
| other names |
IMA 1981-011 |
| chemical formula | Ca 6 Fe 3+ 2 [(OH) 12 | B (OH) 4 | (SO 4 ) 2 ] · 25H 2 O |
|
Mineral class (and possibly department) |
Sulfates (and relatives, see classification ) |
|
System no. to Strunz and to Dana |
7.DG.15 ( 8th edition : VI / D.13) 04.32.04.02 |
| Crystallographic Data | |
| Crystal system | trigonal |
| Crystal class ; symbol | ditrigonal-pyramidal; 3 m |
| Room group (no.) | P 31 c (No. 159) |
| Lattice parameters | a = 11.188 Å ; c = 21.91 Å |
| Formula units | Z = 2 |
| Frequent crystal faces | {10 1 0}, {10 1 4}, {11 2 4} |
| Physical Properties | |
| Mohs hardness | 2.5 |
| Density (g / cm 3 ) | measured: 1.847; calculated: 1.855 |
| Cleavage | completely according to {10 1 0} |
| Break ; Tenacity | brittle |
| colour | yellow, yellowish green, orange brown to greenish brown |
| Line color | light yellow |
| transparency | transparent to translucent |
| shine | Glass gloss, weak greasy gloss on fractured surfaces |
| Crystal optics | |
| Refractive indices |
n ω = 1.499 to 1.500 n ε = 1.497 to 1.505 |
| Birefringence | δ = 0.002 |
| Optical character | uniaxial alternating |
Sturmanite is a very rarely occurring mineral from the mineral class of " sulfates (including selenates, tellurates, chromates, molybdates and wolframates)". It crystallizes in the trigonal crystal system with the chemical composition Ca 6 Fe 3+ 2 [(OH) 12 | B (OH) 4 | (SO 4 ) 2 ] · 25H 2 O.
Sturmanite is transparent to translucent and usually develops hexagonal, dipyramidal crystals with a tabular to prismatic habit . Undamaged crystal surfaces have a glass-like gloss , whereas fracture surfaces tend to have a weak greasy sheen .
Etymology and history
Sturmanite was first discovered in the "Black Rock Mine" on the manganese fields of the Kalahari in South Africa and described in 1983 by Donald R. Peacor , Pete J. Dunn and Marjorie Duggan . They named the mineral after the Slovenian-Canadian mineralogist Bozidar Darko Sturman (* 1937) to honor his contributions to systematic mineralogy, in particular his studies of the phosphate minerals from the Yukon and his refinement of the methods in optical mineralogy.
classification
Already in the meanwhile outdated, but still in use 8th edition of the mineral systematics according to Strunz , the Sturmanite belonged to the department of "Hydrous sulfates with foreign anions ", where together with bentorite , buryatite , carraraite , charlesite , ettringite , jouravskite and thaumasite it forms the "ettringite -Group "with the system no. VI / D.13 .
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 the Sturmanite in the category of "sulfates (selenates, etc.) with additional anions, with H 2 O". However, this is further subdivided according to the relative size of the cations involved and the additional anions that predominate in the compound, so that the mineral is classified in the sub-section “With large to medium-sized cations; with NO 3 , CO 3 , B (OH) 4 , SiO 4 or IO 3 "is to be found, where it is also together with bentorite, birunite , buryatite, carraraite , charlesite , ettringite, jouravskite, corkinoite and thaumasite the" ettringite group “With the system no. 7.DG.15 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Sturmanite to the class of "sulfates, chromates and molybdates" and there in the department of "composite sulfates". Here he is together with Carrarait, Charlesit, Jouravskit and Thaumasit in the " Charlesit group " with the system no. April 32, 2004 to be found in the subsection “ Compound sulfates (containing water) with polyanionic formula”.
Education and Locations
Sturmanit formed secondarily in cavities of metamorphisierter , sedimentary manganese - deposits . As Begleitminerale occur among others barite , ettringite , Hausmannite , hematite and manganite on.
In addition to its type locality , the “Black Rock Mine”, the mineral could also be found in the “Wessels Mine” near Hotazel and in the “N'Chwaning Mines” near Kuruman in the Kalahari manganese fields of South Africa. The “N'Chwaning Mines”, where crystals up to 14 centimeters long were found, are known for their extraordinary sturmanite finds, although crystals up to 40 centimeters in size are also said to have been observed.
The only other previously known site is Mount Lakargi in the Russian Republic of Kabardino-Balkaria .
Crystal structure
Sturmanite crystallizes trigonal in the space group P 31 c (space group no. 159) with the lattice parameters a = 11.188 Å and c = 21.91 Å as well as 2 formula units per unit cell .
use
Even if Sturmanit forms large, transparent, beautifully colored and therefore sharpenable crystals, it is unsuitable as a gemstone for commercial trade due to its low hardness and perfect cleavage . For collectors, however, the mineral is occasionally cut into different facet shapes.
See also
literature
- DR Peacor, PJ Dunn, M. Duggan: Sturmanite, a ferric iron, boron analogue of ettringite , In: The Canadian Mineralogist , Volume 21 (1983), pp. 705-709
Web links
- Mineral Atlas: Sturmanite (Wiki)
Individual evidence
- ^ A b Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 411 .
- ↑ a b c Webmineral - Sturmanite
- ↑ a b c American Mineralogist Crystal Structure Database - Sturmanite (2004)
- ↑ a b c d Sturmanite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 64.5 kB )
- ↑ a b c Mindat - Sturmanite
- ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 150 ( Dörfler Natur ).
- ^ Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1600 unique pieces . 13th revised and expanded edition. BLV Verlags-GmbH., Munich et al. 2002, ISBN 3-405-16332-3 , p. 242 .