Poudretteit
| Poudretteit | |
|---|---|
 |
|
| General and classification | |
| other names |
IMA 1986-028 |
| chemical formula | KNa 2 B 3 Si 12 O 30 |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.CM.05 ( 8th edition : VIII / E.22) 63.02.01a.08 |
| Similar minerals | Apatite , beryl , cordierite , milarite , quartz |
| Crystallographic Data | |
| Crystal system | hexagonal |
| Crystal class ; symbol | 6 / mmm |
| Space group | P 6 / mcc (No. 192) |
| Lattice parameters | a = 10.329 (1) Å ; b = 13.485 (3) Å |
| Formula units | Z = 2 |
| Frequent crystal faces | {100} |
| Physical Properties | |
| Mohs hardness | 5 |
| Density (g / cm 3 ) | measured: 2.51; calculated: 2.53 |
| Cleavage | Please complete |
| Break ; Tenacity | splintery to mussel-like |
| colour | colorless, pale pink |
| Line color | White |
| transparency | translucent to cloudy |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n ω = 1.516 (1) n ε = 1.532 (1) |
| Birefringence | δ = 0.016 |
| Optical character | uniaxial positive |
| Pleochroism | strong: ω = violet pink ε = colorless, pale brown |
The mineral poudretteite is a very rare ring silicate from the milarite group and has the chemical composition K 1.00 (Na 1.87 K 0.04 ) B 3.05 Si 12.14 O 30 .
Poudretteite crystallizes with hexagonal symmetry and forms isometric to prismatic crystals . It is usually colorless with a glass-like sheen and can be colored pale pink due to trace amounts of manganese and lithium . With a Mohs hardness of 5, poudretteite is about as hard as apatite .
Etymology and history
Like many other minerals of the milarite group, poudretteite is also very similar in its optical and physical properties to other, widespread minerals such as quartz , apatite or apophyllite . Presumably that is why it was overlooked for a long time. As early as the mid-1960s, M. Jacques Bradley collected poudretteite- containing marble - xenolites in the syenite - breccia of the Poudrette mine on Mont Saint-Hilaire in Québec , Canada . It took around 20 years for them to be recognized and described as a new mineral. Joel D. Grice , T. Scott Ercit , Jerry van Velthuizen and Pete J. Dunn named the new member of the milarite group after the Poudrette family who operate the quarry on site.
It took another 14 years until this very rare mineral was recognized and described at another location. In November 2000, an Italian gemstone dealer in Mogok, Myanmar, bought a 3-carat, pink-purple, faceted stone from a local dealer who could not classify it mineralogically. The stone was sent to Eduard Josef Gübelin's gemstone laboratory in Switzerland for identification, where it was identified as Poudretteit.
classification
In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the poudretteit belongs to the general division of " ring silicates (cyclosilicates)", where it is used together with almarudite , armenite , berezanskite , brannockite , chayesite , darapiosit , dusmatovite , eifelite , emeleusite , Faizievit , Merrihueit , Oftedalit , Osumilith , Osumilith- (Mg) , Roedderite , Shibkovite , Sogdianite , Sugilite , Trattnerite , Yagiit and Yakovenchukit- (Y) the " Milarite-Osumilite-Group " with the system no. VIII / E.22 forms.
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 classifies Poudretteit in the "ring silicates" section. This is, however, further subdivided according to the structure of the rings, so that the mineral can be found in the sub-section "[Si 6 O 18 ] 12− -six double rings" according to its structure . With Almarudit, Armenit, Berezanskit, Brannockit, Chayesit, Darapiosit, Dusmatovit, Eifelit, Friedrichbeckeit , Klöchit , Merrihueit, Milarit, Oftedalit, Osumilith, Osumilith- (Mg), Roedderite, Shibkattit, Sogdianit, Sugilite, Sogdianit belongs to the Sugilite " Milaritgruppe " with the system no. 9.CM.05 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Poudretteit to the class of "silicates and germanates", but there in the more finely divided division of "ring silicates: condensed rings". Here it is in the " Milarite Osumilith Group (Milarite Osumilith Subgroup) " with the system no. 63.02.01a can be found in the subsection “ Ring Silicates : Condensed, 6-membered Rings”.
Crystal structure
Poudretteite crystallizes hexagonally in the structure of milarite in the space group P 6 / mcc (space group no.192 ) with the lattice parameters a = 10.239 (1) Å and c = 13.485 (3) Å as well as two formula units per unit cell .
The silicate double rings (T1 position) are completely covered with Si 4+ and B 3+ is exclusively located on the T2 tetrahedron position. The tetrahedral coordination of boron is unusual for minerals that were not formed under high pressures. Most of the time, boron is incorporated in trigonal-planar coordinated lattice positions, e.g. B. in tourmaline .
Poudretteite is the mineral of the milarite group with the highest charge of the tetrahedral framework and the positions in the framework channels and cages are either empty or occupied by simply charged cations. As with almost all minerals of the milarite group, potassium + is in the 12-fold coordinated C position. The 9-fold coordinated B-position is empty and the octahedral A-position is fully occupied by Na + .
Education and Locations
Poudretteite forms contact metamorphic in marble that has been altered by alkali-rich igneous rocks or pegmatitic melts. So far (2016) only two occurrences have been documented worldwide.
In the type locality on Mont Saint-Hilaire in Québec, Canada, poudretteite occurs in marble xenolites in nepheline syenite together with pectolite , apophyllite , quartz and aegirine .
In the vicinity of Mogok, Mandalay , Myanmar , syenitic magmas intruded into calcareous sediments. In the skarn - mineralization at the contact of syenitic melts with surrounding marble is Poudretteit place together with diopside , scapolite , spinel , corundum , andalusite , Kornerupin , Montebrasite and Hackmanit or nepheline, taaffeite , Jeremejewit , corundum and chrysoberyl .
use
The very rare poudretteite from Myanmar achieve gem quality in terms of transparency, color and size and are traded as gemstones.
See also
literature
- Poudretteite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 64.3 kB )
Web links
- Mineral Atlas: Poudretteit
- Mindat - Poudretteite
- Webmineral - Poudretteite
- RRUFF Database-of-Raman-spectroscopy - Poudretteite
- American-Mineralogist-Crystal-Structure-Database - Poudretteite
Individual evidence
- ↑ a b c d e f g h i j k l m n JD Grice, TS Ercit and J. van Velthuizen, PJ Dunn (1987) Poudretteite, KNaB3Si12O3, A New Member Of The Osumilit Group From Mont Saint-Hilaire, Ouebec, And Its Crystal Structure In: Canadian Mineralogist , 25, pp. 763–766 ( PDF, 556 kB )
- ↑ a b Poudretteite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 64.3 kB )
- ↑ a b c CP Smith, G. Bosshart, S. Graeser, H. Hänni, D. Günther, K. Hametner and EJ Gübelin (2003) Poudretteite: A Rare Gem Species from the Mogok Valley In: Gems & Geology , 39, P. 24–31 ( PDF, 349 kB ( Memento of the original dated February 6, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. )
- ↑ Mindat - Locality Pyant Gyi
- ↑ Mindat - Kyauk-sin (Rock Elephant)
