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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
Photo courtesy of Scott Davies, americanthai.com

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.


Colorless to pink, purple



Crystal habit

As stubby, barrel shaped prismatic or bipyramidal crystals

Chemical composition

KNa2B3Si12O30 Potassium sodium boron silicate


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



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.


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.


None observed


Inclusions may include veils of two-phase (liquid + gas) inclusions and localized parallel flat tubes.


None known


None known


None known


Poudretteite is a very rare gem and no special vulnerablities are reported, besides its brittleness.


None known


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

External links