Fontarnauite is a relatively recently described, rare sulfate, borate mineral with the chemical formula . It is found in an evaporite boron deposit. It coexists with other evaporite boron minerals, especially probertite. It is monoclinic, crystallizing in the space group P21/c.García-Veigas, J., Rosell, L., Alcobé, X., Subias, I., Ortí, F., Gündoğan, İ., and Helvaci, C., 2010. Fontarnauite, a New Sulphate-Borate Mineral from the Emet Borate District (Turkey). Revista de la Sociedad Española de Mineralogía 13, 97-98Mindat
It was named for Ramon Fontarnau i Griera, a materials scientist of the University of Barcelona.
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