Hyalophane

Infobox mineral
name = Hyalophane
category = Tectosilicate
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formula = (K,Ba) [Al(Si,Al)Si₂O₈]
molweight = 302.06 gm
color = colorless, yellow, white, red
habit = crystalline - fine - occurs as well-formed fine sized crystals; massive - uniformly indistinguishable crystals forming large masses
system = monoclinic
twinning = commonly simple twins according to the Carlsbad, Manebach, or Baveno laws
cleavage = {001} perfect, {010} imperfect
fracture = brittle - generally displayed by glasses and most non-metallic minerals
tenacity = brittle
mohs = 6 – 6½
luster = vitreous (glassy)
polish =
refractive = "n_α" = 1.542, "n_β" = 1.545, "n_γ" = 1.547
opticalprop = biaxial (-)
birefringence = δ = 0.005
dispersion = weak
pleochroism = colorless
fluorescence=
absorption =
streak = white
gravity = 2.81
density =
melt =
fusibility =
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references = [http://www.mindat.org/min-1960.html Hyalophane: Hyalophane mineral information and data ] ] [ [http://webmineral.com/data/Hyalophane.shtml Hyalophane Mineral Data ] ] [http://rruff.geo.arizona.edu/doclib/hom/hyalophane.pdf] [http://www.museums.udel.edu/mineral/mineral_site/collection/alphabetical/H/hyalophane.html Hyalophane ] ]

Hyalophane or jaloallofane is a crystalline mineral with chemical formula (K,Ba) [Al(Si,Al)Si₂O₈] and a hardness of 6 – 6½. It is part of the feldspar group of tectosilicates, and is considered a barium-rich potassium feldspar. [ [http://www.britannica.com/eb/article-9041681/hyalophane hyalophane - Britannica Online Encyclopedia ] ] "Hyalophane" comes from the Greek "hyalos", meaning "glass", and "phanos" meaning "to appear".

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.

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

References

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