Petalite

The mineral Petalitos (also Castorit or Kastorit ) is a rarely occurring sheet silicate with the composition LiAl [ Si4O10 ]. It crystallizes in the monoclinic crystal system and develops rarely well -formed crystals with dicktafeligem to säuligem habit. He usually can be found in the form of leafy, fissile or massive mineral aggregates. In pure form, the mineral is colorless and transparent. Through multiple refraction due to lattice defects or polycrystalline training but it can also appear white and accept by foreign admixtures a yellowish gray and rarely reddish or greenish color, the transparency decreases accordingly. However, the stroke color is always white. Visible crystal faces have a glass-like luster, cleavage surfaces shimmer contrast nacreous.

With a Mohs hardness of 6 to 6.5 it corresponds roughly to the reference mineral orthoclase, then, to just scratch even with a steel file.

Special Features

Before the blowpipe Petalitos colors the flame red.

With borax it melts to a white translucent pearl and with sodium ammonium phosphate (Sal microcosmicum ) gives a yellowish-white, fine -bubbled pearl. He is impervious to acids and dissolves difficult in nitric acid.

Etymology and history

Was first discovered the mineral on Uto near Nyköping in the Swedish province of Södermanland County ( Södermanland ) and described in 1800 by José Bonifácio de Andrada e Silva, who named it after the Greek word πέταλον [ petalon ] by sheet, to indicate its perfect cleavage.

The Swedish chemist Johan August Arfwedson discovered in 1817 in the first Petalitos the element lithium.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Petalitos belonged to the mineral class of " silicates and Germanates " and then to the Department of " framework silicates ( tectosilicates ) " where he along with Lisitsynit and Virgilit the unnamed group VIII / J.03 formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Petalitos also included in the category of " silicates and Germanates " and there in the department of " layer silicates ( phyllosilicates ) ". This division, however, is further divided according to the structure of the layers, so that the mineral is found in accordance with its construction in the subdivision of " simple networks of six- rings, connected by M, M, etc. ," where it is the only member of the unnamed group 9.EF.05 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the Petalitos in the class of " silicates and Germanates " there, however, in the already fine divided department of the " layer silicates: Two-dimensional infinite layers with other than six -membered rings " one. Here he is the only member of the unnamed group 72.06.01 within the subdivision " layer silicates: Two-dimensional infinite layers with other than six -membered rings: tetrahedral Al interconnects " to find.

Education and Locations

Petalitos forms in lithium-containing granite pegmatites. Accompanying minerals occur among others albite, lepidolite, microcline, pollucite, quartz, spodumene, topaz and various tourmalines.

A rare mineral formation Petalitos could be proven so far only in a few localities, where so far (as of 2012) are about 90 localities known as. Apart from its type locality Uto in Södermanland the mineral in Sweden was still at Ultevis in Lapland, at Järkvissle and Västanå in the municipality of Sundsvall ( Medelpad ) and in the Åkerberg mine and Varuträsk in the municipality of Skellefteå ( Västerbotten ).

Known localities include Bikita in Zimbabwe and Varuträsk in Sweden, where crystal masses of several meters length came to light. In Paprok in Afghanistan about 20 cm large crystals were found and Araçuaí ( Minas Gerais ) in Brazil crystals with about 10 cm in diameter.

Other localities lie among others in Angola, Ethiopia, West Australia, China, Finland, France, Italy, Japan, Canada, Mozambique, Myanmar, Namibia, Portugal, Russia, the Czech Republic, the United Kingdom ( UK) and the United States of America (USA ).

Crystal structure

Petalitos crystallizes in the monoclinic space group P2 / a ( Raumgruppen-Nr. 13) with the lattice parameters a = 11.74 Å; b = 5.17 Å; c = 7.63 Å and 112.5 ° and β = 2 formula units per unit cell.

Use

Petalite is - next to spodumene and Lepidolithglimmer - an important source of lithium. Otherwise, the mineral is mainly known in collector circles. Colourless variants are occasionally cut as a gem (it's also a variety Petalitos cat eye known)