A very small specimen of the very rare Na-K-V oxide mineral bannermanite from the type locality in Izalco volcano, El Salvador, where it is extremely rare. Analyzed spciemen by SEM/EDS. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Bannermanite
Bannermanite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Na,K)ₓV⁴⁺ₓV⁵⁺₆₋ₓO₁₅ (0.5<x<0.9).
It crystallizes in the monoclinic crystal system (space group C2/m).
Key properties: specific gravity 3.5; Dark gray-black streak; Submetallic luster; optically biaxial.
IMA symbol Bnm, IMA status: approved, named in 1980.
Found in vanadium-bearing sublimates in fumaroles on a basaltic volcanic cone.
It is found associated with Shcherbinaite, stoiberite, ziesite, fingerite, chalcocyanite, chalcanthite.
The mineral was named to honor Dr. Harold MacColl Bannerman (1897–1976), American economic geologist, U.S. Geological Survey and Dartmouth College, Hanover, New Hampshire, USA.