Hackmanite from Mont Saint-Hilaire, Canada

Hackmanite from Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada

Specimen pieces of the uncommon mineral Hackmanite from Mont Saint-Hilaire.

Hackmanite is a variety of Sodalite with an unusual optical property, tenebrescence. Tenebrescence is the changing of colour when exposed to sunlight.

In most cases, the mineral is purple when originally mined, and fades to colourless when exposed to sunlight. This can be reversed by leaving the specimen in a dark place for some time - sometimes up to a month. They are also brightly fluorescent under UV light.

These pieces are a pale colourless/grey colour but the colour can be restored by leaving them in the dark for an extended period.