Idolite
| Idolite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | NaCa 6 Ti (Si 2 O 7 ) 2 OF 3 |
|
Mineral class (and possibly department) |
Silicates and germanates - group silicates (sorosilicates) |
|
System no. to Strunz and to Dana |
9.BE.22 ( 8th edition : VIII / C.12) 56.02.05.04 |
| Crystallographic Data | |
| Crystal system | triclinic |
| Crystal class ; symbol | triclinic pinacoidal; 1 |
| Space group | P 1 (No. 2) |
| Lattice parameters |
a = 9.67 Å ; b = 5.73 Å; c = 7.33 Å α = 90.0 °; β = 101.0 °; γ = 101.3 ° |
| Formula units | Z = 1 |
| Twinning | lamellar twins according to {001} |
| Physical Properties | |
| Mohs hardness | 5 to 6 |
| Density (g / cm 3 ) | measured: 3.03 to 3.14; calculated: [2.84] |
| Cleavage | perfect after {100}, good after {001} |
| Break ; Tenacity | brittle |
| colour | colorless, white, honey yellow |
| Line color | White |
| transparency | transparent |
| shine | Greasy shine |
| Crystal optics | |
| Refractive indices |
n α = 1.651 to 1.662 n β = 1.653 to 1.665 n γ = 1.659 to 1.672 |
| Birefringence | δ = 0.008 to 0.010 |
| Optical character | biaxial positive |
| Axis angle | 2V = measured: 38 to 74 °; calculated: 62 to 68 ° |
Götzenit is a rarely occurring mineral from the mineral class of "silicates and germanates" with the idealized chemical composition NaCa 6 Ti (Si 2 O 7 ) 2 OF 3 and is therefore a sodium - calcium - titanium - silicate with additional oxygen and fluorine ions . Structurally, the mineral belongs to the group silicates (sorosilicates).
Since a part of the calcium by sodium and a part of fluorine by at natural Götzeniten hydroxide diadoch replaced can be and be able to represent the arrangement of the chemical constituents to one another better, the composition also will crystal Chemical structural formula Ca 4 (Ca, Na) 2 NaTi [(F, OH) 4 | (Si 2 O 7 ) 2 ] or Na (Na, Ca) 4 Ca 2 Ti [(O, F) 2 | (Si 2 O 7 ) 2 ].
Götzenite crystallizes in the triclinic crystal system and develops mostly needle-like to prismatic crystals with a fat-like sheen on the surfaces, but also occurs in the form of granular mineral aggregates and lamellar crystal twins . In its pure form, idol is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white and take on a honey-yellow color due to foreign admixtures, whereby the transparency decreases accordingly.
Etymology and history
Götzenit was first discovered together with Combeit in 1954 on Mount Saheru, the southern summit of the Nyiragongo volcano near Goma (North Kivu Province) in the Democratic Republic of the Congo and described in 1957 by Thure Georg Sahama and Kai Hytönen . They named the mineral after the German East Africa researcher and governor of the former colony of German East Africa Gustavus Adolphus of idols , in 1894 the first white man boarded the Nyiragongo and Mount Saheru.
Type material of the mineral is in the Natural History Museum in London, England (catalog number 1957,702), the Royal Museum for Central Africa in Tervuren, Belgium (catalog number RGM8037) and the National Museum of Natural History in Washington, DC, USA (Catalog No. 142981).
classification
Already in the outdated but still partially in use 8th edition of the mineral classification by Strunz of Götzenit belonged to the mineral class of "silicates and Germanates" and then to the Department of "group silicates (Sorosilikate)" where he collaborated with Hainit , Kochit , mosandrite , Nacareniobsit - (Ce) , Rinkit and Rosenbuschit the "Mosandrite-Rosenbuschit series" with the system no. VIII / C.12 formed.
The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also classifies the Götzenite in the category of "group silicates (sorosilicates)". However, this is further subdivided according to the structure of the silicate groups, the possible presence of additional anions and the coordination number of the cations involved , so that the mineral is classified in the sub-section “Si 2 O 7 groups with additional anions; Cations in octahedral [6] and greater coordination ”can be found, where only together with Hainite, Kochit and Rosenbuschit the“ Rosenbuschitgruppe ”with the system no. 9.BE.22 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the idolsite to the class of "silicates and germanates" and there in the department of "group silicates: Si 2 O 7 groups and O, OH, F and H 2 O" a. Here it is together with dovyrenite , fersmanite , mosandrite, nacareniobsite (Ce), rinkite and roumaite in the " Mosandrite and allied species " with the system no. 56.02.05 within the subsection "Group silicates: Si 2 O 7 groups and O, OH, F and H 2 O with cations in [4] and / or> [4] -coordination".
Crystal structure
Götzenite crystallizes triclinic in the space group P 1 (space group no. 2) with the lattice parameters a = 9.67 Å ; b = 5.73 Å; c = 7.33 Å; α = 90.0 °; β = 101.0 ° and γ = 101.3 ° and one formula unit per unit cell .
Education and Locations
Idolsite forms in volcanic rocks such as nephelinite , but also metamorphically in horn rock and marble . Depending on the locality can be used as accompanying minerals among others Aegirin , apatite , Cancrinit , combeite , Fersmanit , fluorite , Pektolith and sphene occur.
As a rare mineral formation, Götzenite could only be detected at a few sites, whereby so far (as of 2014) around 20 sites are known. In addition to its type locality Mount Saheru on Nyiragongo , the mineral was only found in the Republic of the Congo in the so-called bingo carbonatites ( Bingu Carbonatites ) in the Kivu region .
In Germany, Götzenite has so far only been found in the Fohberg quarry near Bötzingen in Baden-Württemberg and in several places around Mendig , Daun , Roth and the Laacher See in the Rhineland-Palatinate Vulkaneifel .
Other previously known sites include the Poudrette quarry on Mont Saint-Hilaire and Mont McGerrigle in the municipality of La Haute-Gaspésie in Canada, Werner Bjerge in the Greenland province of Tunu , the Vispi quarry near San Venanzo (Umbria) in Italy, the Ruri complex in the Kenyan province of Nyanza , the quarries of Aris near Windhoek in Namibia, Lowosero tundra and several mountains (Eweslogtschorr, Koaschwa, Kukiswumtschorr in the Chibinen on the Russian Kola peninsula and Norra Kärr in the Swedish municipality of Jönköping ).
See also
literature
- Thure Georg Sahama, Kai Hytönen: Götzenite and Combeite, Two New Silicates from the Belgian Congo . In: Mineralogical Magazine . tape 31 , no. 238 , September 1957, p. 503-510 ( minersoc.org [PDF; 316 kB ]).
- E. Cannillo, F. Mazzi, G. Rossi: Crystal structure of Götzenite . In: Soviet Physics - Crystallography . tape 16 , no. 6 , 1972, p. 1026-1030 ( arizona.edu [PDF; 461 kB ]).
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 694 (first edition: 1891).
Web links
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names; March 2014 (PDF 1.5 MB; Götzenite p. 68)
- ↑ 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. 577 .
- ↑ a b c d Idolite . 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; 72 kB ]).
- ↑ 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 .
- ↑ a b c d e Mindat - Idolite
- ↑ Th. G. Sahama, Kai Hytönen: Götzenite and Combeite, Two New Silicates from the Belgian Congo. In: Mineralogical Magazine. Volume 31, No. 238 (September 1957), pp. 503-510 ( PDF 316.7 kB )
- ↑ Mindat - Number of localities for Götzenite
- ↑ Find location list for Götzenit in the Mineralienatlas and Mindat