Hyalophane

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Hyalophane
Hyalophane011.jpg
hyalophane on matrix (Busovaca, Bosnia and Herzegovina)
General
Category Tectosilicate
Formula
(repeating unit)
(K,Ba)[Al(Si,Al)Si2O8]
Crystal system Monoclinic – Prismatic
Unit cell a = 8.52 Å, b = 12.95 Å, c = 7.14 Å, β = 116° Z=4
Identification
Formula mass 302.06 g
Color Colorless, yellow, white, red
Crystal habit Crystalline – fine – occurs as well-formed fine sized crystals; massive – uniformly indistinguishable crystals forming large masses
Crystal symmetry Monoclinic 2/m
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 – 6½
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 – 6½. 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, in the municipality of Binn, 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 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.[6]

References[edit]

  1. ^ a b "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. ^ a b c "Hyalophane". 
  5. ^ "Hyalophane". Britannica Online Encyclopedia. 
  6. ^ Schumann, Walter (1977). Gemstones of the World. p. 56. ISBN 978-1454909538.