sellaite

Sellaite is a rare mineral composed of magnesium fluoride, with the chemical formula MgF2. It is classified as a halide mineral and typically occurs as colorless to white crystals.

Crystallographically, sellaite forms in the tetragonal crystal system. It generally presents a prismatic habit and a vitreous (glassy) luster. The crystals are usually small and may be transparent to translucent.

Sellaite forms in hydrothermal veins and pegmatites, particularly in fluorine-rich environments. It is often found in association with other fluoride minerals and halides. Because it is relatively uncommon, sellaite is mainly of interest to mineral collectors and researchers studying fluoride-bearing assemblages rather than as a major ore or source of magnesium or fluoride.

In addition to its mineralogical interest, magnesium fluoride has notable industrial uses in optics and high-vacuum applications. However, natural sellaite itself is not typically exploited for these uses, and its significance rests largely on its rarity and its role in the study of halide mineralogy.