Hyalophane

Hyalophane
Hyalophane on matrix (Busovaca, Bosnia and Herzegovina)
General
Category Tectosilicate
Formula
(repeating unit)		 (K,Ba)[Al(Si,Al)Si2O8]
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/m
Unit cell a = 8.52 Å, b = 12.95 Å,
c = 7.14 Å; β = 116°; Z = 4
Identification
Formula mass 302.06 g/mol
Color Colorless, yellow, white, red
Crystal habit Crystalline – fine – occurs as well-formed fine sized crystals; massive – uniformly indistinguishable crystals forming large masses
Twinning Commonly simple twins according to the Carlsbad, Manebach, or Baveno laws
Cleavage {001} perfect, {010} imperfect
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 6 – ​6 1⁄2
Luster Vitreous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.81
Optical properties Biaxial (-)
Refractive index nα = 1.542, nβ = 1.545, nγ = 1.547
Birefringence δ = 0.005
2V angle 48 – 79°
Dispersion Weak
References [1][2][3][4]

Hyalophane or jaloallofane is a crystalline mineral, part of the feldspar group of tectosilicates. It is considered a barium-rich potassium feldspar.[5] Its chemical formula is (K,Ba)[Al(Si,Al)Si2O8], and it has a hardness of 6 – ​6 1⁄2. The name hyalophane comes from the Greek hyalos, meaning "glass", and phanos meaning "to appear".[4]

An occurrence of hyalophane was discovered in 1855 in Lengenbach Quarry, Imfield, Binn valley, municipality of Binn, Canton of Valais, Switzerland. The mineral is found predominantly in Europe, with occurrences in Switzerland, Australia, Bosnia, Germany, Japan, New Jersey, and the west coast of North America.[4] Hyalophane may be found in manganese deposits in compact metamorphic zones.[6]

Hyalophane has a monoclinic crystallography, with cell properties a = 8.52 Å, b = 12.95 Å, c = 7.14 Å, and β = 116°. Optically, the material exhibits biaxial birefringence, with refractive index values of nα = 1.542, nβ = 1.545, and nγ = 1.547 and a maximum birefringence of δ = 0.005. It has weak dispersion and low surface relief.[1]

Hyalophane has sometimes been used as a gemstone.[7]

References

  1. 1 2 "Hyalophane". Mindat.org. Hudson Institute of Mineralogy. Retrieved 11 May 2016.
  2. ↑ "Hyalophane Mineral Data". Webmineral.com. Retrieved 11 May 2016.
  3. ↑ Hyalophane (PDF), Mineral Data Publishing
  4. 1 2 3 "Hyalophane". Archived from the original on 2006-09-01.
  5. ↑ "Hyalophane". Britannica Online Encyclopedia.
  6. ↑ Deer, W. A.; Howie, R. A.; Zussman, J. (2001). Rock-Forming Minerals: Volume 4A: Framework Silicates: Feldspars (2nd ed.). Geological Society of London. p. 928. ISBN 9781862390812. Retrieved 2 December 2016.
  7. ↑ Schumann, Walter (1977). Gemstones of the World. p. 56. ISBN 978-1454909538.
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