The As-rich end-member of the jordanite-geocronite series of the Capillitas Mine, Catamarca

Abstract

The As-rich end-member of the jordanite-geocronite series of the Capillitas Mine, Catamarca. Jordanite, Pb14As6S23, the As-rich end member of the jordanite-geocronite series was found at the Bordón vein, in Capillitas Mine, an epithermal precious- and base-metal vein deposit, located along the eastern slope of the Sierra de Capillitas, Catamarca. It occurs associated with sphalerite, marcasite and galena in anhedral, equidimensional crystals and microcrystalline associations up to 5 mm. It is brittle and its hardness is ~ 3. Under the polarizing microscope, observed with reflected light, it is white with just noticeable birreflectance and pleochroism (bright white to white with a faint grayish hue). Its polishing hardness is lower than that of sphalerite and its reflectivity is high, similar to galena. Jordanite has noticeable anisotropy (in air) with bluish-green and violet with pale ochraceous tint, internal reflections were not observed. Its chemical composition, expressed in weight percent is (min-max-average): S: 17.20-18.49-17.84; As: 10.32-11.44-10.88, Pb: 70.60-71.46-71.03 and Sb: 0.00%. The structural formula, calculated in base of 43 atoms per unit cell, is: Pb14.20As5.80S23.00. Jordanite has monoclinic symmetry , space group P21/m, its strongest X-ray diffraction lines are (dÅ, hkl, I/Io): 2.287, 1 12 1, 100; 1.819, -1 17 1, 80; 3.17, 2 6 0, 60; 2.111, -2 1 4, 50. The unit cell parameters, refined from powder diffraction data using CELREF, are: a = 8.933 (2) Å, b = 31.869 (4) Å, c = 8.458 (1) Å, ß = 117.17°, V = 2131 (1) Å3.