Some yellow brown single crystals of the very rare mineral Na silicofluoride mineral malladrite from the TL in Vesuvius (Mount Vesuvius, Campania, Italy) in a capsule. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Malladrite
Malladrite is an IMA-recognized mineral species in the halide class, with the chemical formula Na₂SiF₆.
It crystallizes in the hexagonal crystal system (space group P321). It is a member of the Malladrite structural group.
Key properties: specific gravity 2.755; optically uniaxial.
IMA symbol Mld, grandfathered status — known before the IMA’s founding, named in 1926.
Found as a volcanic sublimate.
It is found associated with Avogadrite, hieratite, sal ammoniac, ferruccite, sassolite (Vesuvius, Italy); barberiite, sassolite (Vulcano, Italy).
The mineral was named to honor Professor Alessandro Malladra (1868–1945), Italian vulcanologist, Director, Vesuvius Observatory, Italy.