Sellaite

Sellaite is a relatively rare magnesium fluoride mineral with the chemical formula MgF₂. It crystallizes in the tetragonal crystal system, typically forming colorless or white crystals, but can also occur in shades of yellow, pink, or gray due to impurities. The crystals are usually prismatic or granular.

Sellaite is named after Quintino Sella (1827-1884), an Italian mineralogist and statesman.

Geologically, sellaite is found in a variety of environments, including hydrothermal veins, pegmatites, and sedimentary rocks. It is often associated with other fluoride minerals, such as fluorite, and may occur as a secondary mineral formed by the alteration of magnesium-bearing minerals. Notable occurrences of sellaite include locations in Italy, Germany, and the United States.

Sellaite is used in some industrial applications, primarily as a source of magnesium and fluorine. It is also of interest to mineral collectors due to its relative rarity and varied crystal forms. Its refractive index and birefringence make it useful in certain optical applications, though its rarity limits widespread usage.