Lepidolite

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Lepidolite
Lepidolite-76774.jpg
Lepidolite, Virgem da Lapa, Minas Gerais, Brazil (size 2.4 x 2.1 x 0.7 cm)
General
Category Silicate mineral
Formula
(repeating unit)
K(Li,Al)3(Al,Si,Rb)4O10(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 is a lilac-gray or rose-colored member of the mica group with formula K(Li,Al,Rb)3(Al,Si)4O10(F,OH)2.[1][2] It is a secondary source of lithium. It is a phyllosilicate mineral[3] and a member of the polylithionite-trilithionite series.[4]

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.[5] 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.[6]

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.

References[edit]

  1. ^ a b c Handbook of Mineralogy
  2. ^ a b Webmineral
  3. ^ Hurlbut, Cornelius S.; Klein, Cornelis (1985), Manual of Mineralogy, Wiley, (20th ed.) ISBN 0-471-80580-7
  4. ^ Lepidolite on Mindat.org
  5. ^ H. Nechamkin, The Chemistry of the Elements, McGraw-Hill, New York, 1968.
  6. ^ 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.