CONICET | Buscador de Institutos y Recursos Humanos

The description of the danburite from the first occurrence of Argentina is reported. Danburite is found as an hydrotermal mineral in the iron (copper)mine of the Nevado de Acay. It is formed in magmatic-hidrotermal environment of porphyry copper related skarn. The mineral occurs as crystal which measure < 1.5 cm in joints of a calc-silicate hornfels, near of the skarn. It is associated with garnet, tourmaline, quartz, minor magnetite and epidote. The crystals are prismatic according to [001] with diamond shaped cross sections. They have {100}, {010}, {110} and {120} as common crystallographic forms and several {hk0} vicinal planes. The parameters of the unit-cell computed from powder X-ray data are: a0 = 8.048, b0 = 8.741, c0 = 7.710, V = 542 Å3 and the principal reflections: 3.58 (I/I0 = 100), 3.45 (80), 2.74 (80), 2.651 (70), 3.87 (70). The crystals are generally white and traslucent with some parts colorless and transparent; they have {001} very indistict cleavage and a measure density of 2.961 gr/cm3. Its optical properties are: bxa(-), 2Vcalc = 90º, dispersion v>r very strong, α = 1.630(3), β = 1.633(3), γ = 1.636(3), X = a, Y = c, Z = b. The chemical composition of this danburite is SiO2 = 48.75, Al2O3 = 0.14, B2O3 = 29.27, CaO = 21.84 which gives Ca0.95B2O3(Si0.99O4)2. Key words: danburite, hydrothermal, chemistry, XRD, IR.

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