In this paper we have summarised data from representative collection of plagioclase compositions (56 wet chemistry and 142 microprobe analyses) from various rock types of different intrusions within the Talnakh ore field. It is shown that chemical composition of plagioclase covers whole solid solution between albite and anortite. No clear relationships have been established between plagioclase composition and magnesium number of host rocks. This is related to zonal structure and polychronic formation of the studied complexes, as well as problems with analytical data. Our estimations suggest that about 10% of used plagioclase analyses are characterized by random or systematic errors. Refs 20. Figs 4.