БАРИЕВЫЙ БИОТИТ ИЗ ИЛЬМЕН

Abstract

The reported find of barium biotites at the Aspen cape of the Bolshoy Ishkul lake is the first one at the Urals. These minerals occur in labrador and bytownite biotite-amphibole gabbro forming non-metamorphosed inclusi-ons in blocks of serpentinite melange among metamorphic rocks of Ilmenogorsky complex. There ate two varie-ties of barium biotites: first - with a moderate Ba content (BaO 1.37 wt%), and second - the Ba-rich one (BaO 8.52 wt%). Their crystal-chermical formulas, calculated on 7 cations, are, respectively: I - (K0,98 Ba0.04)1.02 (Mg1.40 Fe2+0.81 Fe3+0.37 Ti0.25 AlVI0.14 Mn0.03 V0.03)3.01 (Si2.74 AIVI1.26O10) (OH)1.37; II - (K0.73 Ba0.27)1.00(Mg1.63 Fe2+0.54 Fe3+0.43 AlVI0.19 Ti0.19 Mn0.02)3.00 (Si2.50 AlVI1.50O10) (OH1.72 C10.04)1.76- Previously, the barium biotites with similar com-positions have been described in Coldwell alkaline complex (Ontario, Canada). It is probable that those bioti-te-amphibole and fassaite gabbro, with such specific biotites, may represent the rocks from bottom levels of the earth's crust, which were lifted up to surface by the serpentinite protrusions.