Pebble rock is a sometimes used term for SiO2 - rich sedimentary rocks. The name comes from the obsolete name for silica silica, which is used also for the resulting formed minerals such as quartz, chalcedony (SiO2) and opal (SiO2 · nH2O ). Pebble rocks are formed either primarily by the accumulation of sedimentary siliceous organisms shells ( radiolarite, diatomaceous earth or diatomite) or by secondary formation of concretions during diagenesis. In such later silicified sedimentary rocks (eg limestones, sandstones, or breccias ) provides that the SiO2 phase, either finely dispersed in the rock matrix or in the form of nodules ( flint, chert ) on.
Related terms are siliceous (obsolete), siliceous marl, Kieseloolith, pebbly sandstone (obsolete) and chert (deprecated).
Today pebble rocks are summarized under the English technical term Chert.