Lepidolite

minerals

polylithionite

mica

trilithionite

Images
Lepidolite is a series between polylithionite and trilithionite Formulae:
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
Common impurities in polylithionite: Ti,Fe,Mn,Mg,Ca,Na,H2O
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).

At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, lepidolite is rare, but in some pockets muscovite is overgrown by lepidolite. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.510).

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