Grothite from schists of the Irtysh shear zone (East Kazakhstan)

Grothite, a rare fluorine-alumina variety of titanite, was found and studied in the shales of the Irtysh shear zone (Eastern Kazakhstan). The mineral composition was defined Tescan Vega3 scanning electron microscope (SEM). The Al2O3 and F contents, which are not typical for titanite, allowed classifing it as Al-F titanite (grothite). In addition to alumina and fluorine, the studied grothite contains FeO and Y2O3. The general formula of the mineral is as follows: (Ca0.94-1.02Y0.02-0.04Fe0.01-0.02)Ʃ0.99-1.04(Ti0.83-0.89Al0.11-0.16)Ʃ0.94-1.02(Si0.95-0.99Al0.01-0.05)Ʃ1.00O4(O0.86-0.91F0.09-0.14)Ʃ1.00. The maximum contents of Al2O3 and F are characteristic of the central parts of large grains of grothite from muscovite-biotite schists, and the minimum for small grains of grothite from biotite schists, which, apparently, reflects lower pressure parameters during the formation of the latter. The mineral composition of the shales and the low alumina contents in the grotite may indicate the possibility of its crystallization in the rocks of the greenschist facies.