Thortveitite
| Thortveitite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (Sc, Y) 2 Si 2 O 7 |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.BC.05 ( 8th edition : VIII / C.01) 55.02.01a.04 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | C 2 / m |
| Lattice parameters |
a = 6.65 Å ; b = 8.616 Å; c = 4.686 Å β = 102.2 ° Please complete the source as an individual reference |
| Twinning | often, perpendicular to {110} |
| Physical Properties | |
| Mohs hardness | 6 to 7 |
| Density (g / cm 3 ) | 3.27 to 3.58 |
| Cleavage | completely along {100} |
| Break ; Tenacity | uneven to scalloped |
| colour | brown, gray-black, black, grayish green, blue |
| Line color | Gray |
| transparency | semi-transparent |
| shine | glass-like |
| Crystal optics | |
| Refractive indices |
n α = 1.750 to 1.756 n β = 1.789 to 1.793 n γ = 1.802 to 1.809 |
| Birefringence | δ = 65 ° 30 ' |
Thortveitite is a rarely occurring mineral from the mineral group of silicates and germanates . It crystallizes in the monoclinic crystal system with the chemical composition (Sc, Y) 2 Si 2 O 7 and forms prismatic, up to 35 cm large crystals of gray-green to black color. Sometimes you can also find colorless or blue crystals.
Etymology and history
The mineral was found in 1911 by the Norwegian mineralogist Olaus Thortveit in the type locality Ljosland in the Norwegian province of Aust-Agder and described by J. Schetelig. It is named after Thortveit.
classification
In the Strunz system , thortveitite is counted among the group silicates . After the 8th edition, it forms a group together with Gittinsite , Keiviit- (Y) , Keiviit- (Yb) , Kristiansenit , Percleveit- (Ce) , Rowlandite- (Y) and Yttrialite- (Y) . In the 9th edition , it forms with gittinsite, keivit (Y), keivit (Yb) and yttrialite (Y) a subgroup of the group silicates with Si 2 O 7 groups and without non-tetrahedral anions. The cations are in octahedral [6] and / or other coordination.
In the classification by Dana it forms with calcium oxide, manganosite, Monteponit, periclase, wustite and Hongquiit the Periklasgruppe, a subset of simple oxides having a cationic charge of 2+.
Modifications and varieties
Various other elements can be substituted for scandium in thortveitite. These include in particular yttrium , lanthanoids such as ytterbium and lutetium , but also up to 10% thorium , zirconium , hafnium , calcium or manganese can be included. Manganese is responsible for a blue coloration of thortveritite, which is found in the granite of Baveno in Italy .
Education and Locations
Thortveitite forms in granitic pegmatite dikes. The complexation of scandium with fluorine as [ScF] 2+ probably plays a role in the formation. Depending on where it was found , the mineral is associated with euxenite , biotite , oligoclase , microcline and quartz ; Monazite , fergusonite , ilmenorutil , beryl , muscovite and magnetite or cobeit , perrierite , tourmaline , euxenite, monazite, zircon , allanite , magnetite and ilmenite .
Another occurrence is some calcium-aluminum-rich inclusions (CAI) from carbonaceous chondrites . In the Murchison meteorite , thortveitite occurs together with panguit , vanadium-rich davisite and spinel . It is believed that thortveitite is one of the first minerals to resublimate from the hot gas phase during the early phase of the formation of the solar system when the presolar nebula cools .
There are (as of February 2010) 48 sites known for thortveitite. In addition to the type locality and other finds in the Norwegian provinces of Aust-Agder , Finnmark and Telemark , the mineral can be found in the Obersulzbachtal in Austria , Paraíba in Brazil , Marathon in Canada , Linwu in China , Pello in Finland , Luzenac in France , Thiemendorf in Germany , several locations in Italy , Kyoto Prefecture in Japan , Befanamo in Madagascar , Świdnica in Poland , the Urals and the Kola Peninsula in Russia , several locations in Sweden, and Ravalli County and Odgensburg in the United States .
Crystal structure
Thortveitite crystallizes in the monoclinic crystal system in the space group C 2 / m with the lattice parameters a = 6.65 Å ; b = 8.616 Å; c = 4.686 Å and β = 102.2 ° as well as one formula unit per unit cell . The Si 2 O 7 anions are in the form of corner-sharing double tetrahedra . These are edge-linked with ScO 6 octahedra and occur in layers in the crystal structure.
use
Thortveitite is an important scandium mineral.
See also
Individual evidence
- ^ New Dana Classification of Halide Minerals
- ↑ a b c Eckard Amelingmeier: Thortveitit . In: Römpp Chemistry Lexicon. Thieme Verlag, as of May 2005.
- ↑ Chi Ma, John R. Beckett, Oliver Tschauner and George R. Rossman: THORTVEITITE (Sc2Si2O7), THE FIRST SOLAR SILICATE? In: Meteoritics and Planetary Science . 46 (S1), 2011, pp. A144 ( caltech.edu [PDF; 96 kB ; accessed on February 20, 2019]).
- ↑ Thortveitite at mindat.org (Eng.)
literature
- Thortveitite in: Anthony et al .: Handbook of Mineralogy , 1990, 1, 101 ( pdf ).
- Eckard Amelingmeier: Thortveitite . In: Römpp Chemistry Lexicon. Thieme Verlag, as of May 2005.
- L. Smart, E. Moore: Introduction to Solid State Chemistry . Vieweg Verlag, 1997.
