Pict. 1.6. Permian black, bitumenous limestone                         Pict. 1.7. Pleistocene limestone

The Folk classification use the type of components to classify limestones. Allochemical rocks are those that contain grains brought in from elsewhere (i.e. similar to detrital grains in clastic rocks). Orthochemical rocks are those in which the carbonate crystallized in place. Allochemical rocks have grains that may consist of fossiliferous material, ooids, peloids, or intraclasts. These are embedded in a matrix consisting of microcrystalline carbonate (calcite or dolomite), called micrite, or larger visible crystals of carbonate, called sparite. Sparite is clear granular carbonate that has formed through recrystallization of micrite, or by crystallization within previously existing void spaces during diagenesis. The name of the rock contains the type of the orthochemical and allochemical components (example oosparite, biomicrite) (Báldi 1991, Haas 1998) (Table 1.2.).

The Dunham classification is based on the concept of grain support. The classification divides carbonate rocks into two broad groups, those whose original components were not bound together during deposition and those whose original components formed in place and consist of intergrowths of skeletal material (Table1.3.).

Siliceous rocks are significant on the surface also. Siliceous sedimentary rocks are almost entirely composed of silica (SiO₂), typically as chert, opal, chalcedony or other microcrystalline forms. Chert is a mineralogically simple rock consisting of microcrystalline quartz. Deposits of chert formed from the accumulation of siliceous skeletons from microscopic organisms such as radiolaria and diatoms. It varies greatly in colour (from white to black), but most often manifests as grey, brown, greyish brown and light green to rusty red; its colour is an expression of trace elements present in the rock, and both red and green are most often related to traces of iron (in its oxidized and reduced forms respectively). There are numerous varieties of chert, classified based on their visible, microscopic and physical characteristics (Báldi 1991, Szakmány 2008a) (Pict.1.8, 1.9).