In this study, we propose a new classification of rocks of the Bazhenov Formation based on the proportions of four principal components (siliceous, clay, and carbonate minerals and organic matter (kerogen)) of mostly biochemogenic and, to a lesser extent, allothigenic origin. The classification is based on the results of mineralogical and chemical analyses of more than 400 core samples from 15 wells drilled within the Bazhenov Formation, West Siberian petroleum basin. Four major classes of rocks, divided into 16 subclasses, have been recognized. The terms mixtite and kerogen-rich rock are introduced. Mixtites (biochemogenic mixtites) are defined as a class of rocks containing less than 50% of each component, including kerogen. It was shown that the most common rocks of the Bazhenov Formation are siliceous-argillaceous, kerogen-siliceous, and kerogen-argillaceous-siliceous mixtites and kerogen silicites, which together account for ~65% of all samples analyzed. The proposed approach can be used to study organic-rich black shales in different sedimentary basins worldwide.