Lepidolite

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Lepidolite

Lepidolite, Virgem da Lapa, Minas Gerais, Brazil. Size 2.4 x 2.1 x 0.7 cm.
General
Category Silicate mineral
Chemical formula KLi2Al(Al,Si)3O10(F,OH)2
Strunz classification 09.EC.20
Crystal symmetry Monoclinic H-M symbol: 2/m
Space group: C 2/m,Cm
Unit cell a = 5.209(2) Å b = 9.011(5) Å
c = 10.149(5) Å;
β = 100:77(4)°; Z = 2
Identification
Color Pink, purple, rose-red, violet-gray, yellowish, white, colorless
Crystal habit Tabular to prismatic pseudohexagonal crystals, scaly aggregates and massive
Crystal system Monoclinic
Twinning Rare, composition plane {001}
Cleavage {001} perfect
Fracture Uneven
Mohs scale hardness 2.5–3
Luster Vitreous to pearly
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.8–2.9
Optical properties Biaxial (-)
Refractive index nα=1.525–1.548, nβ=1.551–1.58, nγ=1.554–1.586
Birefringence 0.0290–0.0380
Pleochroism X = almost colorless; Y = Z = pink, pale violet
2V angle 0° - 58° measured
References [1][2]

Lepidolite (KLi2Al(Al,Si)3O10(F,OH)2 is a lilac-gray or rose-colored phyllosilicate mineral of the mica group that is a secondary source of lithium.[3] It is associated with other lithium-bearing minerals like spodumene in pegmatite bodies. It is one of the major sources of the rare alkali metals rubidium and caesium.[4] In 1861 Robert Bunsen and Gustav Kirchhoff extracted 150 kg of lepidolite and yielded a few grams of rubidium salts for analysis, and therefore discovered the new element rubidium.[5]

It occurs in granite pegmatites, in some high-temperature quartz veins, greisens and granites. Associated minerals include quartz, feldspar, spodumene, amblygonite, tourmaline, columbite, cassiterite, topaz and beryl.[1]

Notable occurrences include Brazil; Ural Mountains, Russia; California, United States; Tanco Mine, Bernic Lake, Manitoba, Canada; and Madagascar.

[edit] References

  1. ^ a b http://rruff.geo.arizona.edu/doclib/hom/lepidolite.pdf Handbook of Mineralogy
  2. ^ http://webmineral.com/data/Lepidolite.shtml Webmineral
  3. ^ Hurlbut, Cornelius S.; Klein, Cornelis (1985), Manual of Mineralogy, Wiley, (20th ed.) ISBN 0-471-80580-7
  4. ^ H. Nechamkin, The Chemistry of the Elements, McGraw-Hill, New York, 1968.
  5. ^ G. Kirchhoff, R. Bunsen (1861). "Chemische Analyse durch Spectralbeobachtungen". Annalen der Physik und Chemie 189 (7): 337–381. Bibcode 1861AnP...189..337K. doi:10.1002/andp.18611890702. 
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