Avogadrite

(repeating unit)(K,Cs)BF₄IMA symbolAvg^[1]Strunz classification3.CA.10Crystal systemOrthorhombicCrystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)Space groupPnmaUnit cella = 8.6588, b = 5.48
c = 7.0299 [Å]; Z = 4IdentificationColorColorless to white, yellowish to reddishCrystal habitTabular to platy octagonal crystals, tiny crystals, elongateLusterVitreous, greasyDiaphaneityTranslucentSpecific gravity2.9Optical propertiesBiaxial (-)Refractive indexn_α = 1.3239, n_β = 1.3245, n_γ = 1.3247Birefringenceδ = 0.0012V angle75°(meas), 58° (calc)Other characteristicsBitter tasteReferences^[2][3][4]

Avogadrite ((K,Cs)BF₄) is a potassium-caesium tetrafluoroborate in the halide class. Avogadrite crystallizes in the orthorhombic system (space group Pnma) with cell parameters a 8.66 Å, b 5.48 Å and c Å 7.03.

The mineral was discovered by the Italian mineralogist Ferruccio Zambonini in 1926. He analyzed several samples from the volcanic fumaroles close to Mount Vesuvius and from the Lipari islands. In nature, it can only be found as a sublimation product around volcanic fumaroles.^[2] He named it after the Italian scientist Amedeo Avogadro (1776–1856).^[5]

• Palache, P.; Berman H.; Frondel, C. (1960). "Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)" John Wiley and Sons, Inc., New York, pp. 97-98.

PF₆⁻, AsF₆⁻, SbF₆⁻ compoundsAlF₆⁻ compoundschlorides, bromides, iodides
and pseudohalogenidesSiF₆^2-, GeF₆^2- compoundsOxyfluoridesOrganofluorideswith transition metal,
lanthanide, actinide, ammoniumnitric acidsbifluoridesthionyl, phosphoryl,
and iodosyl