Hyalophane: Gemstone Infomration

Hyalophane commonly forms in magmatic environments or by contact metamorphism. Most commonly associated with manganese deposits, sometimes in phonolites. Also in hydrothermal Alpine type veins and some pegmatites. It has been reported in veins in pyroxene-amphibole gneisses, in metasedimentary barite deposits (Spain). Notable localities include Switzerland, Australia, Bosnia and Hercegovina (specimens from Alpine type veins at Zagradski Potok near Busovaca are numerous, huge (exceptionally well-developed crystals reach dimensions of over 20 cm and crystals in the 5–10 cm range are not unusual), lustrous and complexly twinned, commonly gemmy), Germany, Japan, Brazil and Slyudyanka, Transbaikal, Siberia, Russia. An exceptional 5-cm transparent  crystal, from the ancient mine Trou des Romains, in Val Sapin, France, has been reported. At Franklin, New Jersey, USA, and in Sweden the hyalophane is red granular.
Appearance
Transparent to translucent. Massive or as prismatic crystals which may show various types of feldspar twinning (Carlsbad, Baveno, etc.)
• Lustre: Vitreous
• Colour: Colorless, yellow, white and red. A green transparent Ba-orthoclase has been reported from south of Felicio dos Santos, Minas Gerais, Brazil.
• Other: Hyalophane probably exhibits the most complex twinning of any species.
Properties
• Crystal system: Monoclinic
• Refractive index: α 1.518–1.580; β 1.521–1.583; γ 1.524–1.586 Biaxial (ve)
• Birefringence: 0.006–0.10
• Density: 2.55–3.1 Celsian20 – Celsian80
• Hardness: 6–6.5
• Cleavage/fracture: Prismatic, perfect to good in two directions at 90°
• Inclusions: Zagradski Potok material may have epigenetic ferruginous staining
• Fluorescence: Some specimens have a weak red fluorescence in SWUV
• Note: May contain ammonium ions that can be detected by IR spectroscopy.