PROBERTITE, Na Ca Bs ° 9 5 Hp, FROM TINCALAYU. SALTA. ARGENTINA.

Abstract

The physical and chemical properties of probertite (Na Ca Bs 09 5 Rz0) found in lhe Tincalayu mine, Salta, Argentina are presented.The mineral is included in dense ulexite, forming nodules till 2 cm in diameter with crystals elongated along [ 001 ] disposed radially measuring till 5mm and 1mm across. Idiomorphie well formed crystals contained in borax and kernite are also found, which have a lenght of O,5mm (e axis ) and a width of 0,1 mm.It is transparent, colorless and has vitreous luster which is very intense in the isolated crystals; it do es not show fluorescence nor phosphorescence. Probertite is monoclinic, 21m; the predominant form is {llO},with{OlO} and {100} quiteless developed, ending with {001}, {101}, (ill} and {111} (indices with the new cellP 2/ a ).Cleavages: {11O} perfect, {010} goodand {1oo} poor; the hardness is 3 1/2, thedensity = 2.133 (measured) and the calculated density 2.130 g cm,3. The mineral is optieally biaxial (+);e< =1.516, B = 1.525, o = 1.546 ± 0.001 (Na light), birefringence = 0.030, 2V = 66° (measured) and 68° (ca1culated); y = b, Z A e = 17°, r > v, elongación (+). Space group P 2 J / a, a = 13.421 (1), b == 12.558 (1), e = 6.591 (1) A, B=100° 01' (S), volumen 1093.9 A3, a: b: e = 1.0687: 1: 0.5248, Z,. 4. The strongest lines in the x-ray powder chart are in A: 9.09 (100), 2.925 (30), 6.61 (28),3.993 (25),4.553 (21), 3.537 (18), 3.304 (17), 1.803 (17), 2.885 (16) and 2.835 (13).A chemical analysis gives wt %: CaO 13.56; MgO 0.09; Nap 9.47;BP3 46.45; Hp 26.96; insoluble 3.47 (by difference); total 100.00.The infrared spectrum is presented; the mineral is slightly soluble in cold and hot water but easily soluble in diluted acid solutions.