| Hyalophane | |
|---|---|
hyalophane on matrix (Busovaca, Bosnia and Herzegovina) |
|
| General | |
| Category | Tectosilicate |
| Chemical formula | (K,Ba)[Al(Si,Al)Si2O8] |
| Crystal symmetry | Monoclinic 2/m |
| Unit cell | a = 8.52 Å, b = 12.95 Å, c = 7.14 Å, β = 116° Z=4 |
| Identification | |
| Molar 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 system | Monoclinic – Prismatic |
| 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 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.[5] 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]