Sellaite

Sellaite is a magnesium fluoride mineral with formula: MgF2. It crystallizes in the tetragonal crystal system typically as clear to white vitreous prisms. It may be fibrous and occur as radiating aggregates. It has a Mohs hardness of 5 to 6 and a specific gravity of 2.97 to 3.15. Refractive index values are nω = 1.378 and nε = 1.390.

It was first described in 1868 and named for Italian mining engineer and mineralogist Quintino Sella (1827-1884). The type locality is Gébroulaz glacier, Val Thorens, Savoie, Rhône-Alpes, France.