Nodular cherts from four stratigrafic profiles of Lower Cretaceous limestones: Rochovica, Kriva, Butkov and Bralo, were studied. The cherts from biomicritic pelagic limestones contain tests of radiolarians mostly replaced by calcite. The cherts are formed microcrystalline quartz (grain size range from 0.1 to 6 µm) with a low crystallinity index (Cl = 1.7 to 3 relative units: Murata & Norman 1976). This range of grain size of quartz is the main condition for the identification of lepisphere textures of mikroquartz precursor - opal-CT. The opal-CT relict textures indicated chert formation by maturation process of silica mineral. We can also present (chert from locality Butkov) a bladed form of the original opal-CT microcrystals, forming the lepispheres. The presence of silica tests in host limestones or also in cherts, suggest biogenic source of chert silica.