Grey brown crystals of the rare mineral gerasimovskite on a contrasting matrix from the type (Karnasurt Mountain, Lovozero Massif, Northern Region, Russian Federation) and only one of the very few localities known worldwide. — Photo: David Hospital · CC BY-SA 4.0
Gerasimovskite
Gerasimovskite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Mn²⁺(Ti,Nb)₅O₁₂·9H₂O.
Key properties: Mohs hardness 2; specific gravity 2.52–2.58; Pearly luster; optically biaxial.
IMA symbol Gms, grandfathered status — known before the IMA’s founding, named in 1957.
Found as a secondary mineral formed by the late-stage hydrothermal alteration of Nb–Ti minerals (possibly epistolite) within ussingite-bearing pegmatites, in association with alkaline intrusions.
It is found associated with Ussingite, epistolite, steenstrupine, neptunite (Lovozero massif, Russia); albite, analcime, aegirine, natrolite, tetranatrolite, chkalovite, lithian mica.
The mineral was named to honor Vasily Ivanovich Gerasimovskii (1911–1979), Russian mineralogist and geochemist, discoverer of many new minerals from the Lovozero massif.