Ramazzoite, [Mg8Cu12(Po4)(Co3)4(OH)24(H2O)20][(H0.33So4)3(H2O)36], the first mineral with a polyoxometalate cation

Ramazzoite (IMA2017-090), [Mg8Cu12(PO4)(CO3)4(OH)24(H2O)20][(H0.33SO4)3(H2O)36], is a new polyoxometalate (POM) mineral from the Monte Ramazzo mine, near Genova, Liguria, Italy. It occurs on magnetite-rich matrix in association with chlorartinite, chrysotile, dypingite, goethite, lepidocrocite and nesquehonite, and is a late-stage, secondary mineral crystallizing from low-temperature, aqueous solutions. Ramazzoite forms as simple cubes up to about 0.15 mm on edge. The mineral is blue to greenish-blue with a vitreous to oily lustre and pale blue streak. Crystals are very brittle with conchoidal fracture, and a perfect cleavage on 100. The Mohs’ hardness is 2½. The measured density is 1.98(1) g cm3. The mineral is soluble with mild effervescence in dilute HCl at room temperature. Optically, ramazzoite is isotropic with n = 1.491(1) (white light). Electron microprobe analyses (with CO2from structural data and H2O from density) gave the empirical formula [(Mg8.00)(Cu8.00Mg3.78)(PO4)(CO3)4(OH)24(H2O)20] [(H0.65S1.01O4)3(H2O)36], based on 1 P atom per formula unit (apfu). Ramazzoite is cubic, P43m, with the unit-cell parameters: a = 13.3887(10) Ǻ, V = 2400.0(5) Ǻ3 and Z = 1. The crystal structure, refined to R1 = 0.064 for 803 observed reflections [I > 2σI], contains a novel [Mg8Cu12(PO4)(CO3)4(OH)24(H2O)20]5+ POM cation.