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Lepidolite

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Definition of Lepidolite

A light mica, lepidolite is Earth’s most common lithium-bearing mineral. Its name is derived from two Greek words: lepidos, which means “scale,” and lithos, which means “stone.” Although typically pale lilac, specimens can also be colorless, violet, pale yellow, or gray. Lepidolite crystals may appear pseudohexagonal. The mineral is also found as botryoidal or kidneylike masses and fine- to coarse-grained, interlocking plates. Its perfect cleavage yields thin, flexible sheets. Lepidolite occurs in granitic pegmatites, where it is associated with other lithium minerals, such as beryl and topaz. The mineral is economically important as a major source of lithium, which is used to make glass and enamels. It is also a major source of the rare alkali metals rubidium and cesium.

Name: From the Greek lepidos for scale, in allusion to its micaceous structure.

Polymorphism & Series: 1M, 2M2 ; 3A polytypes common; 2M1 ; 3M2 rare; a group name.

Mineral Group: Mica group.

Chemical Properties of Lepidolite

Chemical Classification Phyllosilicate
Chemical Composition K(Li,Al)3(Al,Si,Rb)4O10(F,OH)2

Physical Properties of Lepidolite

Color Pink, purple, rose-red, violet-gray, yellowish, white, colorless
Streak White
Luster Sub-Vitreous, Resinous, Greasy, Pearly
Cleavage Perfect {001} perfect
Diaphaneity Transparent, Translucent
Mohs Hardness 2.5 – 4 on Mohs scale
Diagnostic Properties Cleavage
Crystal System Monoclinic
Tenacity Elastic
Fracture Micaceous
Density 2.8 – 2.9 g/cm3 (Measured)    2.83 g/cm3 (Calculated

Optical Properties of Lepidolite

Color / Pleochroism Colorless
Optical Extinction 3-10o
2V: 0° – 58°
Twinning Rare, composition plane f001g, twin axis [310].
Optic Sign Biaxial ({)
Dispersion: r > v; weak.

Occurrence

In granite pegmatites, derived by metasomatic replacement of muscovite or biotite; in some high-temperature quartz veins, greisens, and granites.

Association

Spodumene, elbaite, amblygonite, columbite, cassiterite, topaz, beryl, micas

Uses

Extracted from lepidolite, the metal lithium has many industrial uses, such as in lithium batteries.

Lithium battery

Distribution

Czech Republic. From Alabashka, Ural Mountains, Russia. Sweden. In the USA, at Mt. Mica, near Paris, Oxford Co., and Auburn, Androscoggin Co., Maine; in the MesaGrande and Pala districts, San Diego Co., California; from the Brown Derby pegmatite, Gunnison Co., Colorado; in the Ingersoll mine, near Keystone, Pennington Co., South Dakota. From the Tanco mine, Bernic Lake, Manitoba, Canada. At Maharitra, Mt. Bity, Madagascar. From Bikita, Zimbabwe. In India, at Hazaribagh, Bihar. From the Virgem da Lapa pegmatite, Minas Gerais, Brazil.

References

Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.

Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].

Mindat.org. (2019). Lepidolite: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].

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