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.