Tenebrescent blue sodalite from Mont Saint-Hilaire, Quebec, Canada
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 MSH. I personnally 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've read, technically fluorescent and tenebrescent blue sodalite is actually a fine mixture of blue sodalite and hackmanite, not pure blue sodalite. It is shown here fluorescing under LW, then MW, then SW; the last two pictures show the tenebrescence, and natural color, in white light. It measures 7,8 cm X 7,8 cm X 3,8 cm.
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 in particular.
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 oftenly tenebrescent in all UV wavelengths. Since I don't have decades of experience collecting there, I cannot garantee this is systematically the case.
Natural color of the specimen, in white light.