Sellaite is a magnesium fluoride mineral with the formula MgF2.

Refractive index values are nω = 1.378 and nε = 1.390.

Sellaite was first described in 1868 and named for Italian mining engineer and mineralogist Quintino Sella (1827–1884).

Its type locality is the glacier de Gébroulaz [fr] in France, where it occurred inside bitumen-bearing dolomite-anhydrite clasts within a moraine deposit.

It has been reported in an evaporite deposit at Bleicherode; within volcanic ejecta and fumaroles at Vesuvius; in a metamorphic magnesite deposit at Serra das Éguas [pt]; and in sodic alkali granite near Gjerdingen [no].