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Formula: LiAlSiO4
Inosilicate (chain silicate), phenakite group
Crystal System: Trigonal
Specific gravity: 2.657 to 2.666 measured, 2.654 calculated
Hardness: 6½
Streak: white
Colour: Colourless, white, pale tan, pale grey
Solubility: gelatinises in acids
Common impurities: Na,K
Environments:
Eucryptite occurs in lithium-rich
pegmatites, often as graphic intergrowths with
albite derived from alteration of
spodumene
(Dana.
Alteration
Eucryptite is a secondary mineral derived from
spodumene and associated with
albite, spodumene,
petalite, amblygonite,
lepidolite and quartz.
The co-occurrence of the lithium aluminium silicates
spodumene,
petalite and eucryptite is not common, but it
does occur in some pegmatites in northern Portugal. The
spodumene
precipitates early from the magma,
petalite later, and
eucryptite is hydrothermal and secondary. On alteration
spodumene is
mainly replaced by
albite and muscovite, and
petalite by
K-feldspar and eucryptite
(CM 39.729-746).
spodumene and Na+ to eucryptite, albite
and Li+
2LiAlSi2O6 + Na+ → LiAlSiO4 + NaAlSi3O8
+ Li+
(AM 67: 97-113
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