The name chert is sometimes limited to the finer varieties, and the coarser are called hornstone. Also, the name chert is very commonly given to the siliceous concretions which occur as nodules and layers in limestone rocks, much in the same way as flints in chalk. When these materials exist to such an extent as to render limestone useless for economical purposes, it is said to be "cherty".
Related category• GEOLOGY AND PLANETARY SCIENCE
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