Thomsenolite
| Thomsenolite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | NaCa [AlF 6 ] • H 2 O |
|
Mineral class (and possibly department) |
Fluoride |
|
System no. to Strunz and to Dana |
3.CB.40 ( 8th edition : III / C.02) 06/11/06/01 |
| Similar minerals | Pachnolite , yaroslavite |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic 2 / m |
| Space group | P 2 1 / c |
| Lattice parameters |
a = 5.563 Å ; b = 5.541 Å; c = 16.115 Å β = 96.35 ° Please complete the source as an individual reference |
| Formula units | Z = 4 Please complete the source as an individual reference |
| Physical Properties | |
| Mohs hardness | 2 |
| Density (g / cm 3 ) | measured: 2.981; calculated: 2.986 |
| Cleavage | completely after {001}; clearly after {110} |
| Break ; Tenacity | brittle |
| colour | colorless, white, reddish, brownish |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss to pearlescent |
| Crystal optics | |
| Refractive indices |
n α = 1.407 n β = 1.414 n γ = 1.415 |
| Birefringence | δ = 0.008 |
| Optical character | biaxial negative |
Thomsenolite is a rarely occurring mineral from the mineral class of " fluorides ". It crystallizes in the monoclinic crystal system with the chemical composition NaCa [AlF 6 ] • H 2 O and develops mostly tabular to prismatic-needle-like crystals , rarely radial, stalactitic or massive mineral aggregates and crusty coatings.
Etymology and history
Was first found in 1868 in the thomsenolite cryolite - deposit at Ivittuut (Kitaa) in West Greenland and described by James Dwight Dana , of the mineral in honor of the Danish chemist Hans Peter Jørgen Julius Thomsen named after him.
classification
In the meanwhile outdated system of minerals according to Strunz (8th edition) , Thomsenolite still belongs to the division of "hydrous double halides" without further subdivisions, where it forms a separate group together with pachnolite and yaroslavite.
Since the 2001 restructuring and partial redefinition of the classes in the 9th edition of Strunz's mineral systematics, the mineral can be found in the new section of "Complex Halides" and there in the sub-section of "Island aluminofluorides (Neso-aluminofluorides)" where it only forms the unnamed group 3.CB.40 together with pachnolite .
The systematics of minerals according to Dana , which is common in the English-speaking world , also assigns Thomsenolite to the class of halides, but there in the department of “ Complex halides - aluminum fluorides with different formulas ”, where the mineral is the only member of the unnamed group 06/11/06 .
Crystal structure
Thomsenolite crystallizes monoclinically in the space group P 2 1 / c with the lattice parameters a = 5.563 Å ; b = 5.541 Å; c = 16.115 Å and β = 96.35 ° as well as four formula units per unit cell .
properties
Pure thomsenolite is colorless or white if it is microcrystalline or due to lattice defects. However, it can be caused by foreign additions such. B. various iron oxides of reddish or brownish color.
Modifications and varieties
The chemical compound NaCa [AlF 6 ] • H 2 O is dimorphic . In addition to the Thomsenolite, the pachnolite also consists of the same chemical elements and also crystallizes in the monoclinic crystal system, but in a different space group ( F 2 / d )
Education and Locations
Thomsenolite is secondary to the weathering of cryolite or other alkali - aluminum fluorides in granitic pegmatites . In addition to cryolite and pachnolite, the mineral is also found in paragenesis with ralstonite , chiolite , cryolite ionite , elpasolite , sellaite and fluorite .
In addition to its type locality , the cryolite deposit near Ivittuut in Greenland, Thomsenolite has so far been found at almost 20 sites worldwide (status: 2010): In the "Demix Varennes Pit" near Saint-Amable in Québec , Canada ; in the slag fields at Thorikos in Greece; at Eldfell in Iceland; at “Verkhneje Espe” in the Tarbagatai Mountains in Eastern Kazakhstan ; at Jos (Plateau) in Nigeria; at Gjerdingselva (Gjerdingen) in Marka (Norway) ; in several regions of Eastern Siberia and the Urals in Russia; in the "Perzhanskoe ore field" in the Ukrainian Oblast of Zhytomyr ; as well as in some regions of the USA .
See also
literature
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 492 .
Web links
- Mineral Atlas: Thomsenolite (Wiki)
- Webmineral - Thomsenolite (English)
Individual evidence
- ↑ a b Handbook of Mineralogy - Thomsenolite (English, PDF 70.7 kB)
- ↑ a b Thomsenolite at mindat.org (engl.)
- ↑ Stefan Weiß: The large Lapis mineral directory . 5th edition. Christian Weise Verlag, Munich 2008, ISBN 3-921656-17-6 .
- ↑ Mindat - Localities for Thomsenolite