Inderita MgB3O3(OH)5.5H2O de la mina Santa Rosa, Sijes, Salta, Argentina

MARQUEZ ZAVALÍA, M. F.; GALLISKI, M.A.

Córdoba

Congreso; XIII MinMet y IV PIMA; 2019

Asociación Mineralógica Argentina y Comisión de Petrología (COMPETRO) de la Asociación Geológica Argentina

Inderite was found in botroydal centimetric nodules contained in a sequence of tilted continental pelites from Santa Rosa mine, a playa-lake Tertiary borate deposits located at Sijes, Salta. The mineral occurs in transparent, colorless, prismatic acicular crystals mainly up to 2 mm in length and 50-70 μm in width. Crystals are elongated along [001] with {110}, possibly {120}, {001}, and {0kl} crystallographic forms. Associated minerals are gypsum and inderborite. The cell data show (in Å), a = 6.831(2), b = 13.113(2), c = 12.016(3), β 104.58º(1), V 1041.8 (0.4771)Å3, Z = 4. The mineral is biaxial (+) with α = 1.488(1), β = 1.491(1), γ = 1.504(1), 2Vcalc = 51.7º, dispersion r > v moderate. Optical orientation is X = b, Z ^ c = 8º. The chemical composition gives (wt. %): B2O3 = 36.68, MgO = 14.52, Na2O = 0.50, H2O = 48.80, Ins. = 1.04. The mineral was possibly formed by the interaction of boron-rich, volcanic derived brines, with Mg-rich tuffitic material intercalated in the sedimentary sequence.