Study of mineralogical variability of ferruginous quartzites of productive strata of the eastern wing of the Petrovsky synclinal fold with using diagram Mm-Mo. (2019). Visnyk of V. N. Karazin Kharkiv National University. Series Geology. Geography. Ecology, 50, 54-62. https://doi.org/10.26565/2410-7360-2019-50-04