Tenebrescent Blue Sodalite - Mont Saint-Hilaire, Quebec, Canada
Contributed by: FMS Admin
minID: YH7-QRM
Date: May 17th, 2026
Locality: Poudrette quarry (De-Mix quarry; Demix quarry; Uni-Mix quarry; Carrière Mont Saint-Hilaire; MSH), Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada (See on Mindat)
Size: 7.8 x 3.8 x 7.8 cm
Description:
Like most fluorescent minerals collectors already know, sadly, blue sodalite is rarely fluorescent. To my knowledge, fluorescent blue sodalite occurs only in Greenland and Afghanistan, and is also found in very small quantities at Mont Saint-Hilaire (MSH). I personally found some only on one occasion (we're talking about a small find here - only one vein in a boulder in a blast pile), during a field trip in 2018.
From what I have read, technically fluorescent and tenebrescent blue sodalite is a fine mixture of blue sodalite and hackmanite, not pure blue sodalite.
Unlike many MSH hackmanite specimens, this specimen is tenebrescent only upon exposure to SW. Some of the best LW tenebrescent hackmanite from MSH is so reactive that it even changes color when left in the sun for a moment; sadly, this is not the case with this specimen.
From what I observed in MSH hackmanite, it seems that the variety which occurs as small grains in the sodalite syenite changes color only when exposed to SW, and the variety that occurs as veins and lenses either in green calc-silicate rock or syenite, or as masses in pegmatite, is more often tenebrescent in all UV wavelengths. Since I do not have decades of experience collecting there, I cannot guarantee this is systematically the case.
Originally posted by Frédéric Messier Leroux on Nature's Rainbows in 2021.
Summary of luminescence responses:
Sodalite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Midwave (305nm LED) UV light: Orange
- Fluorescence under Shortwave (255nm LED) UV light: Red
- Tenebrescence after exposure to Shortwave (255nm LED) UV light: Purple