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| Petalite | |
|---|---|
 Petalite from Minas Gerais State, Brazil (size: 3x4 cm) | |
| General | |
| Category | Phyllosilicate |
| Formula (repeating unit) | LiAlSi4O10 |
| IMA symbol | Ptl[1] |
| Strunz classification | 9.EF.05 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P2/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 |
| 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[2] |
| Fusibility | 5 |
| Solubility | Insoluble |
| References | [3][4][5][6] |
Petalite, also known as castorite, is a lithium aluminum phyllosilicate[7] mineral LiAlSi4O10, crystallizing in the monoclinic system. Petalite occurs as colorless, pink, grey, yellow, yellow grey, to white tabular crystals and columnar masses. It 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.[8] Petalite (and secondary spodumene formed from it) is lower in iron than primary spodumene, making it a more useful source of lithium in, e.g., the production of glass. The colorless varieties are often used as gemstones. [citation needed]
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ "Petalite". Digital Fire. Retrieved 23 October 2011.
- ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Petalite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 14 March 2022.
- ^ Webmineral
- ^ "Petalite". Mindat.org.
- ^ *Hurlbut, Cornelius S. and Klein, Cornelis, 1985, Manual of Mineralogy, Wiley, 20th ed., pp. 459–460 ISBN 0-471-80580-7
- ^ Nickel, Ernest H.; Nichols, Monte C. "IMA/CNMNC List of Mineral Names" (PDF). Internet Archive. Materials Data, Inc. Retrieved 12 December 2024.
- ^ Deer, W. A. (2004). Framework silicates: silica minerals, feldspathoids and the zeolites (2. ed.). London: Geological Soc. p. 296. ISBN 978-1-86239-144-4.