|Chemical composition||KNa2B3Si12O30 Borosilicate|
|Habit||Hexagonal and barrel-shaped etched prisms|
|Optic nature||Uniaxial +|
|Refractive index||1.510 - 1.532|
|Birefringence||0.016 - 0.021|
|Specific gravity||2.50 - 2.55|
|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.
- 1 Color
- 2 Crystal habit
- 3 Chemical composition
- 4 Diagnostics
- 5 Treatments
- 6 Synthetics
- 7 Imitations
- 8 Care
- 9 Phenomenon
- 10 Occurrence
- 11 Sources
- 12 External links
Colorless to pink, purple
As stubby, barrel shaped prismatic or bipyramidal crystals
KNa2B3Si12O30 Potassium sodium boron silicate
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
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.
The birefringence varies from 0.016 to 0.021 and produces a noticable doubling of facets.
Colorless to pink
No known diagnostic spectrum in the visible range.
Inclusions may include veils of two-phase (liquid + gas) inclusions and localized parallel flat tubes.
Poudretteite is a very rare gem and no special vulnerablities are reported, besides its brittleness.
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.
- 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