Petalite

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Petalite
Petalite.jpg
Petalite from Minas Gerais State, Brazil (size: 3x4 cm)
General
Category Phyllosilicate
Formula
(repeating unit)
LiAlSi4O10
Strunz classification 09.EF.05
Crystal symmetry Monoclinic prismatic
H-M symbol: (2/m)
Space group: P 2/a
Unit cell a = 11.737 Å, b = 5.171 Å, c = 7.63 Å; β = 112.54°; Z = 2
Identification
Color Colorless, grey, yellow, pink, to white
Crystal habit Tabular prismatic crystals and columnar masses
Crystal system Monoclinic
Twinning Common on {001}, lamellar
Cleavage Perfect on {001}, poor on {201} with 38.5° angle between the two
Fracture Subconchoidal
Tenacity Brittle
Mohs scale hardness 6 - 6.5
Luster Vitreous, pearly on cleavages
Streak Colorless
Diaphaneity Transparent to translucent
Specific gravity 2.4
Optical properties Biaxial (+)
Refractive index nα=1.504, nβ=1.510, nγ=1.516
Birefringence δ = 0.012
2V angle 82 – 84° measured
Melting point 1350 °C[1]
Fusibility 5
Solubility Insoluble
References [2][3][4][5]

Petalite, also known as castorite, is a lithium aluminium phyllosilicate mineral LiAlSi4O10, crystallizing in the monoclinic system. Petalite is a member of the feldspathoid group. It occurs as colourless, grey, yellow, yellow grey, to white tabular crystals and columnar masses. Occurs in lithium-bearing pegmatites with spodumene, lepidolite, and tourmaline. Petalite is an important ore of lithium, and is converted to spodumene and quartz by heating to ~500 °C and under 3 kbar of pressure in the presence of a dense hydrous alkali borosilicate fluid with a minor carbonate component.[6] The colorless varieties are often used as gemstones.

Discovery and occurrence[edit]

Petalite from Paprok, Nuristan Province, Afghanistan (size: 7.3 x 2.9 x 2.4 cm)

Discovered in 1800, type locality: Utö Island, Haninge, Stockholm, Sweden. The name is derived from the Greek word petalon, which means leaf.[4][7][8]

Economic deposits of petalite ahre found near Kalgoorlie, Western Australia; Aracuai, Minas Gerais, Brazil; Karibib, Namibia; Manitoba, Canada; and Bikita, Zimbabwe.

The first important economic application for petalite was as a raw material for the glass-ceramic cooking ware CorningWare.[citation needed] It has been used as a raw material for ceramic glazes.

References[edit]

  1. ^ "Petalite". Digital Fire. Retrieved 23 October 2011. 
  2. ^ Handbook of Mineralogy
  3. ^ Webmineral
  4. ^ a b Mindat
  5. ^ *Hurlbut, Cornelius S. and Klein, Cornelis, 1985, Manual of Mineralogy, Wiley, 20th ed., pp. 459-460 ISBN 0-471-80580-7
  6. ^ Framework silicates: silica minerals, feldspathoids and the zeolites (2. ed.). London: Geological Soc. 2004. p. 296. ISBN 1-86239-144-0. 
  7. ^ D'Andraba (1800 (Messidor an VIII). "Des caractères et des propriétés de plusieurs nouveaux minérauxde Suède et de Norwège , avec quelques observations chimiques faites sur ces substances". Journal de chimie et de physique 51: 239. 
  8. ^ Sowerby, James (1811). Exotic mineralogy: Or, Coloured figures of foreign minerals: As a supplement to British mineralogy.