INDERBORITE, CaO MgO 3 B203 11 H20, FROM SIJES DISTRICT, SALTA, ARGENTINA.

Abstract

Idiomorphic crystals ofinderborite from Santa Rosa mine, Sijes district, Salta, Argentina, were used for this study. The mineralis monoclinic, c1assPrismatic, 2/m, space groupA 2/a= 19.212 Á, b = 7.445 Á, e = 12.140 Á, /3= 90° 32', a :b : e = 2.5711 : 1 : 1,6306, cell volume 1736.3 Á3, Z = 4, cell content 4 Ca Mg [B303(OH)sh 6 HzÃ? or4 CaO MgO 3B203 11H20.The crystals are colorless, transparent, also whitish gray and translucen~with vitreous luster and diamond shape; they are formed by {100} and {001} predominantand {OOl}minor, measuring up t04 m in length, 2 rnm in width and a thickness of 1rnm. Thestrongestpeaksin thex-ray powderdiagrarn are in Á: 6.07 (100), 6.35 (50), 3.204(47), 3.287 (46),4.51 (27),3.012 (27), 2.428 (20),9.60 (18), 3.127 (13) and 2.251 (13). Inderborite is biaxial (+), a= 1.485,13= 1.514,1= 1.531 ±0.001 Nalight, 2 V=78°, Y=b,X l\a=2°, r>v weak; cleavage {OOl} very good, fragile, hardness 3 112,density 1.932 (meas.) and 1.9325 (calc.) gr cm3 . A chemical analysis gives wt %: CaO 10.92, MgO 7.89, B203 40.96, H20 38.80, insoluble 1.62, total 100.19. Infrared absortion data are presented.