Castellaroite is a rare arsenate mineral with formula Mn3(AsO4)2•4H2O. It is related to the phosphate mineral metaswitzerite. Castellaroite is monoclinic, with space group P21/n. The other natural manganese arsenate hydrate is manganohörnesite, which is an octahydrate. Kampf, A.R., Cámara, F., Ciriotti, M.E., Nash, B.P., Balestra, C., and Chiappino, L., 2015. Castellaroite, IMA 2015-071. CNMNC Newsletter No. 28, December 2015, 1862; Mineralogical Magazine 79, 1859–1864
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