Sellaite, Fluorite Field of view: 10 cm Locality: Clara Mine, Oberwolfach, Ortenaukreis, Freiburg Region, Baden-Württemberg, Germany Description: Sellaite with — Photo: Alessio Piccioni · Public domain
Sellaite
Natural magnesium fluoride — clear tetragonal prisms, sometimes fibrous.
Intro adapted from Wikipedia (CC BY-SA).
Sellaite is an IMA-recognized mineral species in the halide class, with the chemical formula MgF₂.
It crystallizes in the tetragonal crystal system (space group P4_2/mnm). It is a member of the Rutile structural group.
Key properties: Mohs hardness 5; specific gravity 3.15; typically colorless or white; white streak; Vitreous luster; refractive index 1.384; optically uniaxial.
IMA symbol Sel, grandfathered status — known before the IMA’s founding, named in 1868.
Found in a bituminous dolomite-anhydrite rock (Gebroulaz glacier, France); in evaporites (Bleicherode, Germany); in volcanic ejecta and fumarolic deposits (Vesuvius, Italy); in marble (Carrara, Italy).
It is found associated with Fluorite, sulfur, celestine, anhydrite, gypsum, magnesite, quartz.
The mineral was named to honor Quintino Sella (1827–1884), Italian mining engineer and mineralogist.
Collections: Collector Favorites, Rare & Remarkable.