Petalite
| Petalite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Li [4] Al [4] [Si 4 O 10 ] |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.EF.05 ( 8th edition : VIII / J.03) 72.06.01.01 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | P 2 / a (No. 13, position 3) |
| Lattice parameters |
a = 11.74 Å ; b = 5.17 Å; c = 7.63 Å β = 112.5 ° |
| Formula units | Z = 2 |
| Frequent crystal faces | tabular according to {010}, stretched parallel [100] |
| Physical Properties | |
| Mohs hardness | 6 to 6.5 |
| Density (g / cm 3 ) | measured: 2.412 to 2.422; calculated: [2.40] |
| Cleavage | perfect {001}, indistinct after {201} |
| Break ; Tenacity | clamshell; brittle |
| colour | colorless, white, yellowish gray; rarely reddish or greenish |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass luster, pearlescent on cleavage surfaces |
| Crystal optics | |
| Refractive indices |
n α = 1.504 n β = 1.510 n γ = 1.516 |
| Birefringence | δ = 0.012 |
| Optical character | biaxial positive |
| Axis angle | 2V = 82 to 84 ° |
| Other properties | |
| Special features | Thermoluminescence |
The mineral petalite (also castorite or castorite ) is a rarely occurring layered silicate with the composition Li [4] Al [4] [Si 4 O 10 ]. It crystallizes in the monoclinic crystal system and rarely develops well-formed crystals with a thick tabular to columnar habit . It is usually found in the form of leafy, fissile or massive mineral aggregates . In its pure form, the mineral is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white and, due to foreign admixtures, take on a yellowish-gray and rarely also reddish or greenish color, with the transparency decreasing accordingly. However, the line color is always white. Visible crystal surfaces have a glass-like sheen , whereas cleavage surfaces have a mother-of-pearl shimmer.
With a Mohs hardness of 6 to 6.5, it roughly corresponds to the reference mineral orthoclase , so it can just about be scratched with a steel file.
Etymology and history
The mineral was first discovered on Utö near (22 km NE) Nynäshamn in the Swedish province of Södermanland and described in 1800 by José Bonifácio de Andrada e Silva , who named it after the Greek word πέταλον [petalon] for leaf to indicate its perfect cleavage .
The Swedish chemist Johan August Arfwedson was the first to discover the element lithium in petalite in 1817 .
classification
In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Petalitos belonged to the mineral class of "silicates and Germanates" and then to the Department of " framework silicates (tectosilicates)" where he collaborated with Lisitsynit and Virgilit the unnamed group VIII / J.03 formed.
The valid since 2001 and by the International Mineralogical Association used (IMA) 9th edition of Strunz'schen systematic mineral also assigns the Petalitos in the class of "silicates and Germanates" and then in the Department of " phyllosilicates one (phyllosilicates)". This section is, however, further subdivided according to the structure of the layers, so that the mineral can be found in the sub-section “Simple networks of six-fold rings, connected by M [4] , M [8] etc.” according to its structure , where it is forms the unnamed group 9.EF.05 as the only member .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the petalite to the class of "silicates and Germanates", but there in the more finely subdivided division of "layered silicates: two-dimensional unlimited layers with rings other than six-membered". Here he is to be found as the only member of the unnamed group 72.06.01 within the subsection “ Layered silicates: two-dimensional unlimited layers with rings other than six-membered: tetrahedral Al interconnections ”.
Crystal structure
Petalite crystallizes monoclinically in the space group P 2 / a (space group no. 13, position 3) with the lattice parameters a = 11.74 Å ; b = 5.17 Å; c = 7.63 Å and β = 112.5 ° as well as 2 formula units per unit cell .
properties
In front of the soldering tube , Petalit colors the flame red.
With borax it melts into a white translucent pearl and with sodium ammonium phosphate ( Sal microcosmicum ) a yellowish white, fine bubbled pearl results. It is insensitive to acids and only dissolves with difficulty in nitric acid .
Education and Locations
Petalite forms in granite containing lithium - pegmatites . The accompanying minerals include albite , lepidolite , microcline , pollucite , quartz , spodumene , topaz and various tourmalines .
As a rare mineral formation, petalite could only be detected at a few sites, whereby so far (as of 2012) around 90 sites are known. In addition to its type locality Utö in Södermanland, the mineral was also found in Sweden at Ultevis in Lapland , at Järkvissle and Västanå in the municipality of Sundsvall (Medelpad) and in the Åkerberg mine and at Varuträsk in the municipality of Skellefteå (Västerbotten).
Well-known sites include Bikita in Zimbabwe and Varuträsk in Sweden, where crystal masses several meters in length came to light. At Paprok in Afghanistan a good 20 cm large crystals were found and at Araçuaí ( Minas Gerais ) in Brazil crystals with a diameter of about 10 cm.
Other sites are in Angola, Ethiopia, Western Australia, China, Finland, France, Italy, Japan, Canada, Mozambique, Myanmar, Namibia, Portugal, Russia, the Czech Republic, the United Kingdom (Great Britain) and the United States of America (USA ).
use
Along with spodumene and lepidolite mica , petalite is an important source of lithium . Otherwise, the mineral is mainly known to collectors. Colorless variants are occasionally cut as a gemstone (a variety of petalite cat's eye is also known)
literature
- JB d'Andrada : Brief description of the properties and characteristics of some new fossils from Sweden and Norway, along with some chemical remarks about them. In: Alexander Nicolaus Scherer (Ed.): General Journal of Chemistry. Volume 4, 1800, pp. 28-39 ( PDF 2.36 MB ; p. 10).
- Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1600 unique pieces . 13th revised and expanded edition. BLV Verlags-GmbH., Munich et al. 2002, ISBN 3-405-16332-3 , p. 204 .
Web links
- Mineral Atlas: Petalit (Wiki)
Individual evidence
- ↑ a b c d e 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. 685 .
- ↑ Webmineral - Petalite.
- ↑ a b c d e Petalite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF 73.9 kB )
- ↑ a b c d e Mindat - Petalite.
- ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 769 (first edition: 1891).
- ↑ d'Andrada (1800): Brief statement of the properties and characteristics of some new fossils from Sweden ... (see literature)
- ↑ Mindat - Number of localities for petalite.
- ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (= Dörfler Natur ). Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 262 .