Lepidolite

phyllosilicate

lithium

Lepidolite is a series between polylithionite and trilithionite Formula:
Polylithionite: KLi2AlSi4O10F2
Trilithionite: KLi1.5Al1.5(Si3Al)O10F2
Both are phyllosilicates (sheet silicates) mica group
Specific gravity: 2.8 to 2.9
Hardness: 2 to 2½
Streak: White
Colour: Pink, lilac, reddish; The lavender pink colour is due to Mn3+. The colour of the mineral is not an indication of its lithium content.
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Pegmatites (almost exclusively)
Hydrothermal environments

Lepidolite is a comparatively rare mineral, found in almost exclusively in lithium-rich pegmatites, (DHZ 3 p90) usually associated with other lithium-bearing minerals such as pink and green tourmaline, amblygonite, spodumene and zinnwaldite (a series between siderophyllite and polylithionite), as well as topaz, cassiterite, beryl and quartz (DHZ 3 p90).
It is often intergrown with muscovite in parallel layers. It appears that lepidolite forms late in the crystallisation of pegmatites, succeeding the more common muscovite and biotite of the outer pegmatite zones.
Lepidolite has also been reported in granite and aplite, and in high temperature veins which are often tin-bearing (DHZ 3 p90).

Common impurities in the variety polylithionite: Ti,Fe,Mn,Mg,Ca,Na,H2O

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