Tacharanite
| Tacharanite | |
|---|---|
 |
|
| General and classification | |
| chemical formula |
|
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.HA.75 ( 8th edition : VIII / F.19) 72.03.02.06 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | Please complete |
| Lattice parameters |
a = 17.07 Å ; b = 3.65 Å; c = 27.9 Å β = 114.1 ° |
| Formula units | Z = 2 |
| Physical Properties | |
| Mohs hardness | not defined |
| Density (g / cm 3 ) | measured: 2.33 to 2.36; calculated: 2.28 |
| Cleavage | completely after {001} |
| Break ; Tenacity | clamshell; tough |
| colour | milk white, cream colored |
| Line color | White |
| transparency | translucent |
| shine | Glass gloss, matt |
| Crystal optics | |
| Refractive indices |
n α = 1.518 to 1.525 n γ = 1.530 to 1.537 |
| Birefringence | δ = 0.012 |
| Optical character | biaxial positive |
Tacharanite is a rarely occurring mineral from the mineral class of "silicates and germanates". It crystallizes in the monoclinic crystal system with the chemical composition Ca 12 Al 2 [Si 6 O 17 ] 3 · 18H 2 O, so it is chemically a water-containing calcium - aluminum - silicate .
Tacharanite is microcrystalline and is mainly found in the form of fiber bundles and spherulitic aggregates or porcelain-like, cryptocrystalline masses. In its pure form, tacharanite is colorless and transparent, however, due to the multiple refraction of light due to the polycrystalline formation, it usually appears translucent and milky white or cream-colored ( beige ) due to foreign admixtures .
Etymology and history
Tacharanite was first discovered near Portree on the Scottish Isle of Skye and described in 1961 by Jessie M. Sweet, DI Bothwell and DL Williams. They named the mineral after the Gaelic word "tacharan" for changeling , as it changes into a mixture of the minerals tobermorite and gyrolite in the air .
classification
In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the tacharanite still belonged to the department of " chain silicates and band silicates (inosilicates)", where together with clinotobermorite , plombièrit , riversideit and tobermorite, it formed the "tobermorite group" with the system No. VIII / F.19 .
In contrast , the 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), classifies tacharanite under the category of "unclassified silicates". This is further subdivided according to the metals occurring in the compound, so that the mineral can be found according to its composition in the sub-section “With alkali and alkaline earth elements”, where it is the only member of the unnamed group 9.HA.75 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the tacharanite to the category of "layered silicates: two-dimensional unlimited layers with rings other than six-membered". Here it is in the " Tobermorite group (5- and 8-membered rings) " with the system no. 72.03.02 within the sub-section " Layered silicates: two-dimensional unlimited layers with rings other than six-membered: 3-, 4-, or 5-membered rings and 8-membered rings".
Education and Locations
Tacharanite forms in cavities or cracks of olivine - dolerite or other igneous rocks (see also almond stone ). The accompanying minerals include calcite , gyrolite, mesolite , saponite , scawtite , thomsonite , tobermorite and xonotlite .
As a rare mineral formation, tacharanite could only be detected at a few sites, whereby so far (as of 2014) around 40 sites are known. In addition to its type locality Portree (Isle of Skye) in Scotland , the mineral in the United Kingdom (UK) is only known from Carneal in County Antrim in Northern Ireland.
In Germany, Tacharanite has so far only been found in the "Gaulsberg" quarry near Ortenberg in Hesse, in the "Bramburg" quarry near Adelebsen in Lower Saxony and at the Burgkopf near Hoffeld and at the Arensberg near Zilsdorf ( Hillesheim Association ) in the North Rhine-Westphalian Volcanic Eifel .
The only known site in Austria so far is a basalt quarry near Klöch in Styria.
Other previously known sites include several places on the Australian island of Tasmania , Puech de Vermus ( Espalion municipality , Midi-Pyrénées) in France, the Horse Lake in British Columbia and Asbestos ( Les Sources municipality ) in Québec in Canada, and Puyuhuapi in the Chilean province of Aisén , the "Hatrurim Formation" in the Negev desert in Israel, several sites in the Italian metropolitan cities of Genoa and Catania as well as the province of Vicenza , Noaki ( prefecture Shizuoka , Honshū) and Kōchi (Shikoku) in Japan, Kowdor and Syssert in Russia , the volcano Sant Corneli near Fogars de la Selva in Spain, Sümegprága and Uzsa (Uzsabánya) in the Balaton Highlands ( Lake Balaton ) in Hungary and several places in the US states of Idaho , Oregon and Virginia .
Crystal structure
Tacharanite crystallizes monoclinically with an A-centered pseudocell, but so far not specifically defined space group . The lattice parameters are a = 17.07 Å ; b = 3.65 Å; c = 27.9 Å and β = 114.1 ° as well as two formula units per unit cell .
See also
literature
- Jessie M. Sweet, DI Bothwell, DL Williams: Tacharanite and other hydrated calcium silicates from Portree, Isle of Skye. In: Mineralogical Magazine. Volume 332, 1961, pp. 745-753.
- Michael Fleischer: New Mineral Names. In: American Mineralogist. Volume 47, No. 1–2, 1962, pp. 172–174 ( minsocam.org PDF; 209 kB, p. 2).
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 733 (first edition: 1891).
Web links
Individual evidence
- ^ A b c 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. 656 .
- ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 5th completely revised and supplemented edition. Weise, Munich 2008, ISBN 978-3-921656-70-9 .
- ↑ a b Tacharanite. 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)
- ↑ a b Mindat - Tacharanite.
- ↑ Mindat - Number of localities for Tacharanite.
- ↑ Find location list for Tacharanite at the Mineralienatlas and at Mindat .