Perchiazziite, Co2(CO3)(OH)2, a New Member of the Rosasite–Malachite Group from the Monte Ramazzo Mine, Italy

Abstract

ABSTRACT Perchiazziite, ideally Co2(CO3)(OH)2, is a new mineral discovered at the Monte Ramazzo Mine, Genova Province, Liguria, Italy. It occurs as globular aggregates up to 0.1 mm in diameter, composed of very thin fibers. These develop on a matrix composed mostly of goethite and magnetite, in association with calcite and Co-bearing malachite. Aggregates of perchiazziite are pale orange-pink on their outer surfaces but white in thin section. It is translucent with white streak, silky luster, brittle tenacity, and uneven fracture. No cleavage and parting are observed. The Mohs hardness is ∼4. Dcalc. = 3.970 g/cm3. The mean refractive index calculated using the Gladstone-Dale equation is 1.77. The main bands in the Raman spectrum are at 154, 511, 707, 1085, 1526, 3304, aXnd 3479 cm−1. The chemical composition (by electron microprobe; CO2 and H2O by stoichiometry) of perchiazziite is (in wt.%): MgO 1.81, CaO 0.41, MnO 0.32, FeO 0.12, CoO 32.45, NiO 4.02, CuO 5.40, ZnO 25.60, CO2 20.63, H2O 8.42, total 99.18. The empirical formula calculated on the basis of 5 O apfu is: (Co0.93Zn0.67Cu0.15Ni0.12Mg0.10Ca0.02Mn0.01)Σ2.00(CO3)(OH)2. The crystal structure was refined by the Rietveld method. Perchiazziite is monoclinic, space group P21/a, a = 12.1832(16) Å, b = 9.3187(16) Å, c = 3.1570(3) Å, β = 97.165(15)°, V = 355.62(8) Å3, and Z = 4. The strongest lines of the X-ray powder diffraction pattern [d, Å (I, %) (hkl)] are 6.040 (22) (200), 5.073 (38) (210), 3.694 (53) (220), 2.599 (100) (021), 2.535 (26) (420), 2.480 (27) (221̄), 2.140 (26) (231̄), 1.561 (25) (202̄). Perchiazziite is a new member of the rosasite–malachite group.