











Mineralpedia Details for Petalite
Petalite

- Formula
- LiAlSi4O10
- Crystal System
- Monoclinic
- Crystal Habit
- Massive
- Cleavage
- Perfect, Imperfect, None
- Luster
- Vitreous - Pearly
- Color
- colorless, gray, yellow, yellow gray, white
- Streak
- colorless
- Class
- Monoclinic - Prismatic
- Fracture
- Brittle - Conchoidal
- Hardness
- 6-6.5
- WebMineral
- View Petalite
- Mindat
- View Petalite
Petalite from Taquaral, Itinga, Minas Gerais, Brazil

A water clear crystal fragment of this rare lithium aluminosilicate found exclusively in granitic (LCT) pegmatites. Lithium in pegmatites is usually characterized by one of the primary lithium minerals: Spodumene or Petalite and to a lesser extent Amblygonite-Montebrasite. Lithium pegmatites are rare and constitute about 1-2% of all pegmatites. Most lithium pegmatites are zoned and usually occur at the furthest extents from the parent source and usually intrude metamorphic rock. Rarely do the minerals Petalite and Spodumene occur in the same pegmatite since Spodumene is stable at higher pressures and moderate temperature unlike Petalite (high T and moderate P)...then there is the secondary lithium mineral Eucryptite which is stable at low P and T. See Cerny and/or London...
Petalite from Londonderry Lithium deposit, Western Australia, Australia

Dr, David London of University of Oklahoma has shown that pegmatite formation under conditions of silica (quartz) saturated conditions, the lithium aluminum silicates petalite, spodumene and eucryptite are good indicators of the temperature and pressure of formation. Spodumene at equilibrium occurs at high pressure, while petalite at high temperatures, But upon cooling, spodumene is sometimes seen as replacing petalite.
In this specimen thin white laminations can be seen within the otherwise colorless matrix. This is possibly the sort of replacement London has described on pages 55-58 of his "Pegmatites" - a highly recommended resource. Optical work would be required to determine if this replacement occured in this particular specimen.
Petalite from Rubicon mine, Karibib dist., Erongo, Namibia

A pinkish mass of crystalline Petalite.
Petalite from Bikita Pegmatite, Masvingo dist., Zimbabwe
Bluish gray cleavable mass of Petalite, an ore of lithium. Note the compression fractures and the accompanied folding of the crystal probably done while the crystal was in an elastic "toothpaste" condition.
This specimen, like the many in the upcoming special edition on David London's pegmatite study specimens. Note the stuck on-label indicating that the specimen was featured on page 56, figure 4-9a.
Petalite from Tanco pegmatite, Bernic Lake, Manitoba, Canada
White Petalite with a dull to vitreous luster.