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Formula: LiAlSi4O10
Phyllosilicate (sheet silicate), feldspathoid,
lithium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 2.412 to 2.422 measured, 2.4 calculated
Hardness: 6 to 6½
Streak: White
Colour: Colourless, white, grey, pink
Solubility: Insoluble in acids
Common impurities: Mg,Fe,Na,Ca,K,H2O
Environments:
Petalite is found in granite pegmatites and related rocks,
associated with spodumene, tourmaline,
lepidolite, topaz,
microcline, amblygonite,
apatite, pollucite,
columbite, albite variety cleavelandite and
quartz
(Dana, DHZ 4 p274).
Localities
The type locality is the Utö Mines, Utö, Haninge, Stockholm County, Sweden.
The Stankuvatske Li deposit, Ukrainian Shield, Central Ukraine, represents an uncommon case of recrystallised,
fine-grained petalite ± spodumene metamorphosed
pegmatite dykes with LCT
(lithium - cesium -
tantalum) affinity hosted in
amphibolites and metamorphosed
ultrabasic rocks. The metamorphosed
pegmatite dykes show remnants of
primary, pre-metamorphic zoning, with dominant magmatic
albite, K-feldspar,
quartz, lithium-phases (petalite,
spodumene, rarely triphylite and
montebrasite), and accessory
muscovite, fluorapatite,
columbite-(Fe),
tantalite-(Fe), cassiterite,
tantalum-rich rutile,
zinconigrite, ferronigerite,
gahnite, pyrite,
sphalerite and zircon. The parental
magma of the metamorphosed pegmatites was peraluminous, and
enriched in lithium and phosphorus, though relatively poor in
boron and fluorine during the late-magmatic stage. Metasomatic reactions between
residual pegmatite magma and
ultrabasic country rocks resulted in the precipitation of
holmquistite, triphylite,
fluorapatite, tourmaline and
rubidium- and cesium- rich
biotite. Secondary
generations of fine-grained petalite, spodumene,
albite and K-feldspar were formed
during post-magmatic stages.
Indications are that metamorphic recrystallisation of the former lithium-rich
granitic pegmatites
occurred at relatively high-temperature (~600±50°C) and medium-pressure (~0.3−0.4 GPa)
(MM 86.6.863-882).
Alteration
Petalite alters to montmorillonite
(Dana).
petalite to spodumene and quartz
LiAlSi4O10 ⇌ LiAlSi2O6 + 2SiO2
(DHZ 4 p274).
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