Gaultite from Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada

592-U3EGaultite Na₄Zn₂Si₇O₁₈·5H₂O , Serandite NaMn²⁺₂Si₃O₈(OH) , Ussingite Na₂AlSi₃O₈OH , Makatite Na₂Si₄O₈(OH)₂·4H₂O , Sodalite Na₄(Si₃Al₃)O₁₂Cl

Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada

Dimensions: 10 cm x 6 cm x 3 cm
Field of View: 3.1 mm
Largest Crystal Size: 0.9 mm

This is a closeup of the largest and best crystals of gaultite on the holotype for the species. Canadian Museum of Nature specimen CMNMC 81513. In the full view, the upwards pointing arrow indicates the vug containing these crystals. Found in sodalite syenite.

In the full view, serandite is visible as orange cleavages, ussingite as purple patches in the matrix, and matted white makatite is present in the larger, central vug. Gaultite fluoresces bright green under shortwave ultraviolet light. Makatite fluoresces pale greenish white. The dark orange fluorescence is sodalite.

This photograph appears in the Horvath et al. 2019 volume on Mont Saint-Hilaire published by the Mineralogical Association of Canada (S.P. 14).

Mindat.org Photo of the Day - 14th Oct 2025