| Hyalophane | |
|---|---|
 Hyalophane crystal (Busovača,Bosnia and Herzegovina) | |
| General | |
| Category | Tectosilicateminerals,feldspargroup |
| Formula | (K,Ba)[Al(Si,Al)Si2O8] |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-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 orjaloallofane is a crystalline mineral, part of thefeldspar group oftectosilicates. It is considered a barium-rich potassium feldspar.[5] Its chemical formula is(K,Ba)[Al(Si,Al)Si2O8], and it has ahardness of 6 to6+1⁄2. The namehyalophane comes from theGreekhyalos, meaning "glass", andphanos meaning "to appear".[4]
An occurrence of hyalophane was discovered in 1855 inLengenbach Quarry, Imfield, Binn valley, municipality of Binn, Canton of Valais,Switzerland. The mineral is found predominantly inEurope, with occurrences in Switzerland,Australia,Bosnia,Germany,Japan,New Jersey, and the west coast ofNorth America.[4] Hyalophane may be found inmanganese deposits in compactmetamorphic zones.[6]
Hyalophane has amonocliniccrystallography, with cell properties a = 8.52Å, b = 12.95 Å, c = 7.14 Å, and β = 116°. Optically, the material exhibits biaxialbirefringence, withrefractive index values ofnα = 1.542,nβ = 1.545, andnγ = 1.547 and a maximum birefringence of δ = 0.005. It has weakdispersion and low surface relief.[1]
Hyalophane has sometimes been used as agemstone.[7]
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