Santarosaite, CuB2O4, a new mineral with disordered structure from the Santa Rosa mine, Atacama desert, Chile

The new mineral santarosaite (IMA-CNMNC No. 2007-013) has the ideal chemical formula CuB2O4. It is tetragonal with space group I (4) over bar 2d. Cell parameters refined from X-ray powder diffraction data are a = 11.517(8), c = 5.632(6) (angstrom), V= 747(1) angstrom(3). Z = 12. The strongest reflections in the X-ray powder diffraction data are as follows d(obs.)(angstrom) (I, hkl): 3.797 (100, 211), 3.638 (47: 3 1 0) 2.775 (35 7 32 1) 2.572 (26, 420) and 2.501 (26, 411). Santarosaite was found in the Santa Rosa mine, which is located SE of the city of Iquique, Northern Chile. It occurs as vivid blue, vitreous globules up to 60 mu m in size. The blue globules are aggregates of tiny leaf-like crystallites less than 1 mu m thick. The calculated density is 3.96g/cm(3). The refractive index n derived from reflectance measurements is 1.75. Santarosaite is associated with atacamite, malachite, wulfenite and anhydrite. Chemical analyses gave (wt.%) CuO 43.24, PbO 4.48, CaO 0.97, B2O3 45.44. The resulting empirical formula based on 4 anions is (Cu0.86Pb0.03Ca0.02) B2.06O4. Due to voids in the crystal structure and the micro-crystallinity of the santarosaite globules the chemical analyses only add up to 94.13 wt.%. For structural reasons the chemical formula can thus be described as (Cu0.88Pb0.03Ca0.03 square(0.06))B2O4-0.06. The name of the new mineral is for the type locality, the Santa Rosa copper mine.