Avogadrite
Ferruccite (white) on avogadrite (yellow-brownish), picture size: 5 mm
General
Category	Halide mineral
Formula (repeating unit)	(K,Cs)BF₄
IMA symbol	Avg^[1]
Strunz classification	3.CA.10
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnma
Unit cell	a = 8.6588, b = 5.48 c = 7.0299 [Å]; Z = 4
Identification
Color	Colorless to white, yellowish to reddish
Crystal habit	Tabular to platy octagonal crystals, tiny crystals, elongate
Luster	Vitreous, greasy
Diaphaneity	Translucent
Specific gravity	2.9
Optical properties	Biaxial (-)
Refractive index	n_α = 1.3239, n_β = 1.3245, n_γ = 1.3247
Birefringence	δ = 0.001
2V angle	75°(meas), 58° (calc)
Other characteristics	Bitter taste
References	^[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.

History

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]

Bibliography

^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
^ ^a ^b "Handbook of Mineralogy: Avogadrite" (PDF). The Mineralogical Society of America. Archived from the original (PDF) on 2012-02-18. Retrieved 2010-01-09.
^ Avogadrite on Mindat.org
^ Avogadrite data on Webmin
^ Zambonini, Ferruccio (1926). "Sulla presenza, tra i prodotti dell'attuale attività del Vesuvio, di una varietà cesifera del fluoborato di potassio, (On the presence, among the products of Vesuvius, of a caesium-bearing variety of potassium fluoborate), Rend. Accad. Lincei". 6 (III): 644–649. ((cite journal)): Cite journal requires |journal= (help)