Abstract
Surite, Pb(Pb,Ca)1.17(CO3)2(Al,Fe,Mg)2(Si3.67Al0.33)O10(OH)2 is a new clay–mineral species occurring as compact aggregates in the oxidation zone of the lead-zinc-copper deposits of the Cruz del Sur mine, Argentina. Surite is monoclinic, a = 5.22, b = 8.97, c = 16.3A, β = 96.1°, Z = 2; the space group is possibly P21. Color white, luster glossy like talc; streak white, cleavage perfect {001}. Hardness (Mohs) 2–3, density (g/cm3) 4.0 (meas). Optically anisotropic, colorless in thin section; refractive indices α = 1.693(2), γ = 1.738(2); parallel extinction and positive elongation. The wet–chemical analysis gave SiO2 23.58, Al2O3 11.27, Fe2O3 0.41, CaO 4.75, MgO 1.29, K2O none, Na2O 0.77, H2O + 3.33, H2O − 0.39, PbO 45.32,CuO 0.07, CO2 9.45, sum 100.63 percent. The X-ray powder pattern is characterized by a 16A reflection and its integral series to the 11th order. These reflections do not expand upon ethylene glycol treatment. The X-ray powder study and chemical analysis of the dried acid-treated residue showed that this residue corresponds to a dioctahedral smectite. DTA-TG curves in air show an endotherm around 600° accompanied by weight loss, two exotherms at about 700° and 800°, and an endotherm in the 700–800°C region. The two exotherms are not recognized in nitrogen. IR-spectra are composed of the absorption bands of a silicate and carbonate. The structure of surite is based upon a cerussite-like layer with vacant sites for Pb intercalating with a 2:1 silicate layer similar to dioctahedral smectite. The name is for the locality.
