Cordierite and sekaninaite from xenolites in khibiny alkaline massif

摘要

Sekaninaite—the Fe-dominant analog of cordieritewas known since the beginning of XX~th century, but as a mineralspecies it has been described only in 1975 in Dolini Bery (ChechRepublic). Within Khibiny alkaline massif sekaninaite has actuallybeen found for the principal rock-forming minerals in largehornfels xenoamount up to 30 or even 50% of the rock volume,its segregations make about 3 mm, sometimes up to 1 cm in size.Those metamorphic rocks are quite poor in Mg and rich in Fe and,thus, the cordierite-sekaninaite serical formulae of sekaninaitecalculated for minimum and maximum possible quantities of Mg are as following:(Fe_1.70Mg_0.02Mn_0.03)_?1.75Al_4:11Si_5.05O_18 and(Fe_0.77Mg_0.08)?_1.53(Ma_0.48K_0.01)Al_4.04Si_5.08O_18, respectively. IR spectrum and x-ray powder pattern ofsekaninaite are shown in the paper also. Relations among mineralsin the hornfels are characterized. And sekaninaite is consideredthere as an intermediate product of alteration of the xenolith rocks;furthermore, it was destructed by the alkaline metasomatism.