Poudretteite
| Poudretteite | |
|---|---|
| Chemical composition | KNa2B3Si12O30 Borosilicate |
| Crystal system | Hexagonal |
| Habit | Hexagonal and barrel-shaped etched prisms |
| Cleavage | None |
| Fracture | Conchoidal, splintery |
| Hardness | 5-6 |
| Optic nature | Uniaxial + |
| Refractive index | 1.510 - 1.532 |
| Birefringence | 0.016 - 0.021 |
| Dispersion | Unknown |
| Specific gravity | 2.50 - 2.55 |
| Lustre | Vitreous |
| Pleochroism | Colorless to pink, depending on body color |
A very rare gem, first found in Mont St. Hilaire, Quebec, Canada. Named after the Poudrette family who were the operators of the quarry where it was first discovered.
Contents
Color
Colorless to pink, purple
Transparency
Transparent
Crystal habit
As stubby, barrel shaped prismatic or bipyramidal crystals
Chemical composition
KNa2B3Si12O30 Potassium sodium boron silicate
Diagnostics
Poudretteite could be mistaken for feldspar and scapolite.
Feldspar however has a biaxial optical nature and scapolite is uniaxial with a negative optic sign.
Specific gravity
2.51(Measured), 2.53 (Calculated)
Scapolite has a SG range of 2.634 to 2.74 and feldspar has a range of 1.52 to 1.57
Tenacity
Brittle
Refractive Index
nω = 1.516, nε = 1.532
Poudretteite has a uniaxial optical nature with a positive optical sign.
- Scapolite (n = 1.545 - 1.580) also has a uniaxial character, but has a negative optical sign. Although the readings are somewhat high to indicate poudretteite, the birefringence is similar.
- Feldspars (n = 1.52 - 1.57) are biaxial with a positive or negative optical sign.
Birefringence
The birefringence varies from 0.016 to 0.021 and produces a noticable doubling of facets.
Pleochroism
Colorless to pink
Spectroscope
No known diagnostic spectrum in the visible range.
Luminescence
None observed
Magnification
Inclusions may include veils of two-phase (liquid + gas) inclusions and localized parallel flat tubes.
Treatments
None known
Synthetics
None known
Imitations
None known
Care
Poudretteite is a very rare gem and no special vulnerablities are reported, besides its brittleness.
Phenomenon
None known
Occurrence
Poudretteite was originally described in 1987 as minute crystals of no gemological interest at Mont St. Hilaire; the samples had been collected in the 1960’s. In 2000, rough was discovered in the Pain Pyit district, Mogok, Myanmar that cut a 3ct stone that was later determined to be poudretteite. As of 2004, 10 examples of poudretteite had been identified amoung Mogok stones, the largest being a 22ct crystal that was cut into a 9.4ct gem.
Facet grade poudretteite is also found in Mogok, Burma. As of mid-2007, about 30 small pieces of rough have been recovered. Most produce small gems, and clean stones weighing in excess of 1 carat remain elusive. Some gems are pink in tone, but these also are not common.
Sources
- Anthony, John W., Bideaux, Richard A., Bladh, Kenneth W., and Nichols, Monte C. (1990): Handbook of Mineralogy: Mineral Data Publishing, Tucson, Arizona
- Grice, J D, Ercit, T. S., Van Velthuizen, J. and Dunn P. J. (1987) The Canadian Mineralogist Vol. 25 (1987) pp 763-766 Poudretteite, KNa2B3Si12O30, a new member of the osumilite group from Mont Saint-Hilaire, Quebec, and its crystal structure
- Smith, Christopher P., Bosshart, G., Graeser, S., Hanni, H. and Gunther, D. (2003) Gems and Gemology Vol 39 No. 1 Poudretteite: A Rare Gem Species from the Mogok Valley
