Charoite
| Charoite | |
|---|---|
 |
|
| General and classification | |
| other names |
IMA 1977-019 |
| chemical formula | (K, Na) 5 (Ca, Ba, Sr) 8 [(OH, F) | Si 6 O 16 | (Si 6 O 15 ) 2 ] · n H 2 O |
|
Mineral class (and possibly department) |
Chain silicates and band silicates (inosilicates) |
|
System no. to Strunz and to Dana |
9.DG.32 ( 8th edition : VIII / F.35) 70.01.02.03 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic 2 / m |
| Room group (no.) | P 2 1 / m (No. 11) |
| Lattice parameters |
a = 32.11 Å ; b = 19.77 Å; c = 7.23 Å β = 95.85 ° |
| Formula units | Z = 2 |
| Physical Properties | |
| Mohs hardness | 5 to 6 |
| Density (g / cm 3 ) | measured: 2.54; calculated: [2.77] |
| Cleavage | according to (001) good |
| Break ; Tenacity | uneven |
| colour | purple (lilac) and white striped, light brown |
| Line color | White |
| transparency | translucent to opaque |
| shine | Glass gloss to matt |
| radioactivity | hardly measurable |
| Crystal optics | |
| Refractive indices |
n α = 1.550 n β = 1.553 n γ = 1.559 |
| Birefringence | δ = 0.009 |
| Optical character | biaxial positive |
| Axis angle | 2V = 28 to 30 ° (measured); 72 ° (calculated) |
| Pleochroism | colorless |
The mineral Charoit (German correct charoite ) is a rarely occurring chain silicate from the mineral class of the silicates . It crystallizes in the monoclinic crystal system with the general chemical composition (K, Na) 5 (Ca, Ba, Sr) 8 [(OH, F) | Si 6 O 16 | (Si 6 O 15 ) 2 ] · n H 2 O The elements potassium , sodium , calcium , barium and strontium, as well as the hydroxide ion and fluorine within the square brackets, can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the mineral.
Charoit developed translucent to opaque, moderate or fibrous aggregates in violet and white stripes , wherein the stripes are reciprocally vortexed and may sometimes contain dark inclusions. Charoite is a very popular gemstone .
Etymology and history
Violette rocks in the form of blocks were in the area of the river Tschara first discovered in 1948 and erroneously as cummingtonite - slate described (cummingtonite is a magnesium iron silicate, but Charoit and the accompanying minerals containing no magnesium). In the 1960s, the Irkutsk geologist couple Rogow discovered the actual deposit in the area of the watershed between the Tschara and its tributary Tokko . The deposit was examined in detail in the 1970s and the mineral was described in 1976. Since 1978 it has been included in the IMA 's list as a recognized mineral . According to Russian sources, the mineral was named after its occurrence in the catchment area of the Tschara River ( Russian Чара , English transcription Chara ). According to other sources, the name refers to the equally fitting Russian word chary ( чары ), which means pathetic for magic in the sense of charming , bewitching .
classification
Already in the now outdated, but still in use 8th edition of the mineral systematics according to Strunz , the charoite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where it belongs together with canasite , eveslogite , frankamenite , Miserit and Yuksporit formed the unnamed group VIII / F.35 .
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 assigns Charoite to the class of “silicates and germanates” and there to the “chain and band silicates” department. However, this section is further subdivided according to the type of chain formation, so that the mineral can be found according to its composition in the sub-section "Chain and ribbon silicates with 3-periodic single and multiple chains", where it is the only member of the unnamed group 9. DG.32 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the charoite to the class of "silicates and Germanates", but there in the department of "chain silicates: column or tube structures". Here it is together with narsarsukit and caysichit- (Y) in the group of "double cranked chains" with the system no. 70.01.02 within the sub-section " Chain silicates: column or tube structures with column-like silicate units ".
Education and Locations
Charoite forms hydrothermally in volcanic rocks . It is accompanied by various minerals such as aegirine , feldspars , nepheline , quartz and others.
The type locality is the area of the Murun massif ( location ), which is up to 1,452 meters high, on the border between the Russian administrative units of Irkutsk Oblast , the Republic of Sakha (Yakutia) and the Transbaikalia region . It extends about 70 kilometers southeast of the village of Tschara (also Ust-Shuja ) located at the confluence of the Shuja into the Tschara and 40 kilometers west of the urban-type Torgo settlement on the tributary of the Tokko in the Olyokminsk district.
This is practically the only place where it was found, especially in the eastern part of the massif. On the deposit called Sirenewy Kamen ( lilac-colored rock ), the annual extraction of 100 tons is permitted. Theoretically, export from Russia is only allowed in processed form.
Crystal structure
Charoite crystallizes monoclinically in the space group P 2 1 / m (space group no. 11) with the lattice parameters a = 32.11 Å ; b = 19.77 Å; c = 7.23 Å and β = 95.85 ° as well as 2 formula units per unit cell .
use
Charoite is only used as a gemstone, either for jewelry or sculptures . There is a possibility of confusion with amethyst .
See also
literature
- Paul Ramdohr , Hugo Strunz : Textbook of Mineralogy (16th edition), Ferdinand Enke Verlag (1978), ISBN 3-432-82986-8
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0
Web links
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. 641 .
- ↑ Webmineral - Charoite (English)
- ↑ a b c American-Mineralogist-Crystal-Structure-Database - Charoite (2011)
- ↑ a b c d e Mindat - Charoite (English)
- ↑ John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Charoite , in: Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 76 kB )