Avogadrite

Avogadrite
Ferruccite (white) on avogadrite (yellow-brownish), picture size: 5 mm
General
Category Halide mineral
Formula
(repeating unit)		 (K,Cs)BF4
Strunz classification 3.CA.10
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnma
Unit cell a = 8.6588, b = 5.48
c = 7.0299 [Å]; Z = 4
Identification
Color Colorless to white, yellowish to reddish
Crystal habit Tabular to platy octagonal crystals
Luster Vitreous, greasy
Diaphaneity Translucent
Specific gravity 2.9
Optical properties Biaxial (-)
Refractive index nα = 1.3239, nβ = 1.3245, nγ = 1.3247
Birefringence δ = 0.001
2V angle 75°(meas), 58° (calc)
References [1][2][3]

Avogadrite ((K,Cs)BF4) is a potassium-caesium tetrafluoroborate in the halide class. Avogadrite crystallizes in the orthorhombic system (space group Pnma) with cell parameters a 8.66 Å, b 5.48 Å and c Å 7.03.

History

The mineral was discovered by the Italian mineralogist Ferruccio Zambonini in 1926. He analyzed several samples from the volcanic fumaroles close to Mount Vesuvius and from the Lipari islands. In nature, it can only found as a sublimation product around volcanic fumaroles.[1] He named it after the Italian scientist Amedeo Avogadro (1776–1856).[4]

See also

  • Ferruccite, (NaBF4), the sodium tetrafluoroborate.

References

  1. 1 2 "Handbook of Mineralogy: Avogadrite" (PDF). The Mineralogical Society of America. Retrieved 2010-01-09.
  2. ↑ Avogadrite on Mindat.org
  3. ↑ Avogadrite data on Webmin
  4. ↑ Zambonini, Ferruccio (1926). "Sulla presenza, tra i prodotti dell'attuale attività del Vesuvio, di una varietà cesifera del fluoborato di potassio, (On the presence, among the products of Vesuvius, of a caesium-bearing variety of potassium fluoborate), Rend. Accad. Lincei". 6 (III): 644–649.
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