Toturite
| Toturite | |
|---|---|
| General and classification | |
| other names |
IMA 2010-073 |
| chemical formula | Ca 3 Sn 2 Fe 2 SiO 12 |
|
Mineral class (and possibly department) |
Silicates and Germanates |
| Crystallographic Data | |
| Crystal system | cubic |
| Crystal class ; symbol | cubic hexakisoctahedral; 4 / m 3 2 / m |
| Space group | Ia 3 d (No. 230) |
| Lattice parameters | a = 12.55 Å |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | not determined |
| Density (g / cm 3 ) | calculated: ~ 4.49 |
| Cleavage | not determined |
| Break ; Tenacity | not determined |
| colour | yellow or light brown |
| Line color | White |
| transparency | Please complete |
| shine | not determined |
| radioactivity | sometimes weakly radioactive due to uranium incorporation |
| Crystal optics | |
| Refractive index | n = not determined |
| Birefringence | isotropic |
The mineral toturite is a very rare silicate from the upper group of garnets with the idealized chemical composition Ca 3 Sn 2 Fe 2 SiO 12 . It crystallizes in the cubic crystal system with the structure of garnet and is found in small areas or small patches in transformation products of zirconium or Kimzeyit - Kerimasit -rich grenades.
So far (2017) toturite has only been detected in its type locality , a calcium silicate xenolite from an ignimbrite from Mount Lakargi, Chegem Caldera in the North Caucasian republic of Kabardino-Balkaria in Russia .
Etymology and history
Artificially produced tin-rich garnets with up to 26% by weight SnO 2 occur together with cassiterite in slag from tin smelting .
Natural tin-containing garnets are very rare. In a few tin-bearing skarns, andradites with up to 5.8% by weight SnO 2 were found, and the Sn garnets Bitikleit , Dzhuluit and Irinarassite were found in the sanidinite-facial lime-silicate foreign rock inclusions of the ignimbrite of the Chegem Caldera . In this xenolite , Galuskina's group discovered an Sn-Fe silicate garnet. They named the new mineral on the one hand after the river Totur in the village of Eltyubyu near the site, and on the other hand after the Balkar god and warrior of antiquity Totur.
classification
The current classification of the International Mineralogical Association (IMA) counts the toturite to the garnet upper group, where together with kimzeyite , hutcheonite , schorlomite , kerimasite and irinarassite it forms the schorlomite group with 10 positive charges on the tetrahedrally coordinated lattice position.
The outdated, but still in use 8th edition of the mineral classification according to Strunz does not yet list the toturite. He would, together with almandine Andradite , Calderit , Goldmanit , Grossular , Henritermierit , Hibschite , Holtstamit , Hydrougrandit , katoite , Knorringit , majorite , Morimotoit , pyrope , Schorlomit , Spessartin , Uwarowit , wadalite and Yamatoit (discredited because identical to Momoiit ) for " Garnet group "with the system no. VIII / A.08 in the section of " Island Silicates (Nesosilicates)".
Even the 9th edition of Strunz's mineral systematics, which has been in effect since 2001 , does not yet know the toturite. Here it would also be in the "garnet group" with the system no. 9.AD.25 within the division of "Island Silicates (Nesosilicates)". This is further subdivided according to the possible presence of further anions and the coordination of the cations involved , so that the mineral is classified according to its composition in the subsection “Island silicates without additional anions; Cations in octahedral [6] and usually greater coordination ”would be found. The garnets irinarassite , hutcheonite , kerimasite , menzerite (Y) and eringaite described after 2001 would also have been sorted into the garnet group.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , would classify toturite in the category of "island silicate minerals ". Here it would be together with kimzeyite, schorlomite and morimotoite in the "garnet group (schorlomite-kimzeyite series)" with the system no. 51.04.03c within the subsection “ Island silicates: SiO 4 groups only with cations in [6] and> [6] coordination ”.
Chemism
Toturite is the Sn analog of schorlomite and forms complex mixed crystals , especially with kerimasite, schorlomite and dzhuluit. In the type locality, toturite occurs in two variations with the following compositions:
- [X] (Ca 3.016 Mn 2+ 0.004 ) [Y] (Sn 4+ 1.731 Zr 4+ 0.083 Ti 4+ 0.066 U 6+ 0.043 Sc 3+ 0.045 Nb 5+ 0.009 ) [Z] (Fe 3+ 1.353 Al 0.644 Si 0.558 Ti 4+ 0.438 Fe 2+ 0.007 ) O 12 ,
- [X] (Ca 2.989 Fe 2+ 0.011 ) [Y] (Sn 4+ 1.463 Sb 5+ 0.325 Ti 4+ 0.193 Zr 4+ 0.013 Mg 2+ 0.003 Nb 5+ 0.002 Cr 3+ 0.001 ) [Z] (Fe 3 + 1.633 Al 0.609 Si 0.552 Ti 4+ 0.166 Fe 2+ 0.039 V 5+ 0.001 ) O 12
where [X], [Y] and [Z] indicate the positions in the garnet structure.
The compositions of the mixed crystals can be expressed with various combinations of terminal links. Thus, toturite is largely miscible with schorlomite and kerimasite in accordance with the exchange reactions
- [Y] Sn 4+ = [Y] (Ti, Zr) 4+ (Schorlomite, Kerimasite)
as well as the Al 3+ minerals of the schorlomite group irinarassite, hutcheonite and kimzeyite according to the exchange reaction
- [Z] Al 3+ = [Z] Fe 3+ .
In addition, toturite contains up to 16% of the octahedrally coordinated Y-position antimony (Sb 5+ ), corresponding to a mixed crystal formation with ferrite garnets of the bitite-conductive group with the exchange reaction
- [Y] Sn 4+ + [Z] Si 4+ = [Y] Sb 5+ + [Z] (Fe, Al) 3+ (Dzhuluit / Bitikleit).
The Ti contents in the Z position can be added as an admixture of a Ti analogue of Irinarassite, [X] Ca 3 [Y] Sn 4+ 2 [Z] (Al 2 Ti 4+ ) O 12 or its Fe analog according to the exchange reaction
- [Z] Si 4+ = [Z] Ti 4+
to be discribed.
Crystal structure
Toturite crystallizes with cubic symmetry in the space group Ia 3 d (space group no. 230) with 8 formula units per unit cell . The natural mixed crystal from the type locality has the lattice parameter a = 12.55 Å .
The structure is that of garnet . Calcium (Ca 2+ ) occupies the dodecahedral X positions surrounded by 8 oxygen ions, tin (Sn 4+ ) the octahedral Y position surrounded by 6 oxygen ions and the tetrahedral Z position surrounded by 4 oxygen ions is iron (Fe 3+ ) and silicon (Si 4+ ) occupied.
Education and Locations
Toturite forms at low pressure and high temperatures around 800–1000 ° C in contact-metamorphic, Sn-bearing skarns , grown on conversion products of zirconium or as narrow zones in kerimasite.
The type locality of toturite is a carbonate-rich xenolite in the ignimbrite of Mount Lakargi, Chegem Caldera in the North Caucasian republic of Kabardino-Balkaria in Russia . Here toturite occurs in the larnite - cuspidin zone of xenolite number 3 at the contact with ignimbrite. Accompanying minerals are kerimasite-kimzeyite mixed crystals, lakargiite , tazheranite , andradite , wadalite and cuspidin.
See also
Web links
- Mineral Atlas: Toturite (Wiki)
- Mindat - Toturite (English)
Individual evidence
- ↑ a b c d e f g h i j k Irina O. Galuskina, Evgeny V. Galuskin, Piotr Dzierżanowski, Viktor M. Gazeev, Krystian Prusik, Nikolai N. Pertsev, Antoni Winiarski, Aleksandr E. Zadov, Wrzalik Roman: Toturite Ca3Sn2Fe2SiO12 — A new mineral species of the garnet group . In: American Mineralogist . tape 95 , no. 8–9 , 2010, pp. 1305–1311 ( rruff.info [PDF; 1.7 MB ; accessed on October 8, 2017]).
- ↑ Find location list for toturite at the Mineralienatlas and at Mindat
- ^ BCM Butler: Tin-rich garnet, pyroxene, and spinel from a slag . In: Mineralogical Magazine . tape 42 , December 1978, p. 487–492 ( rruff.info [PDF; 464 kB ; accessed on September 25, 2017]).
- ^ Edward S. Grew, Andrew J. Locock, Stuart J. Mills, Irina O. Galuskina, Evgeny V. Galuskin and Ulf Hålenius: IMA Report - Nomenclature of the garnet supergroup . In: American Mineralogist . tape 98 , 2013, p. 785–811 ( main.jp [PDF; 2,3 MB ; accessed on July 8, 2017]).
- ↑ Hisanori Yamane, Tetsuya Kawano: Preparation, crystal structure and photoluminescence of garnet-type calcium tin titanium aluminates . In: Journal of Solid State Chemistry . tape 184 , no. 5 , 2011, p. 965-970 , doi : 10.1016 / j.jssc.2011.02.016 .