siliceous rock

Any of a group of sedimentary rocks that consist largely or almost entirely of silicon dioxide (SiO₂), either as quartz or as chert, the most common siliceous rock. It occurs in beds and in nodules. Bedded cherts may be an original organic or inorganic precipitate. Nodular cherts appear to be produced by the alteration of preexisting sedimentary rock. In this process silica distributed throughout the rock dissolves and reprecipitates to form nodules.

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Siliceous rocks are sedimentary rocks that have silica (SiO₂) as the principal constituent. The most common siliceous rock is Chert other types include Diatomite. They commonly form from silica-secreting organisms such as radiolarians, diatoms, or some types of sponges.