Cacoxenita, Fe3+24AlO6(PO4)17(OH)12·75H2O, del yacimiento Ranquel, distrito pegmatítico Totoral, San Luis, Argentina

Cacoxenite, Fe3+24AlO6(PO4)17(OH)12•75H2O, has been found in the Ranquel Be-bearing pegmatite, located in the Loma Alta group of the Totoral pegmatitic field, San Luis, Argentina. This phosphate mineral occurs as golden to brownish yellow spherulitic aggregates which show internal rosette structure, hosted between vivianite crystals or in small cavities. Optically, the mineral is uniaxial positive, with ω = 1.572, e = 1.642; the pleocroism is weak with O = pale yellow and E = brownish yellow. The strongest lines of the X-ray diffraction powder pattern are [dobs in A(I/I0)(hkl)]: 11.88(100)(200), 13.78(18)(110) and 6.83(12)(121, 211). The unit cell parameters data, derived from least squares refinement, are: a 27.531(8) A, c 10.549(1) A, V 6927(2) A3, with c/ a 0.383. EDS and WDX analyses give P, O, Fe, Mn y Al. Cacoxenite is considered to have been formed in a late hydrothermal stage under high oxidizing conditions