Volcanic clastic rocks comprise various rocks of clastic texture, formed as a result of volcanic activity. Classification of these rocks should be based, in the first place, on petrographical characteristics, which are possible to determine macro- and microscopically. In the suggested classification volcanic clastic rocks are subdivided into four groups, according to the composition of cementing mass and to the relative contents of pyroclastic and sedimentary material, namely: lava breccias, pyroclastic rocks (welded tuffs, tuffs, volcanic breccias), essentially pyroclastic rocks (tuffites) and pyroclastic-sedimentary (tuffogenic-sedimentary) rocks. Further subdivision of the rocks depends on their granulometric composition, chemico-petrographical composition and also on homogeneity or heterogeneity of the clastic material. In some cases there are also taken into account the relative contents of vitric, crystal and lithic pyroclastic material and the degree of abrasion and sorting of the fragments. Resear...