Chert

Chert is a sedimentary rock in the class known as chemical sedimentary rocks. It is composed of microcrystalline quartz.

Chert is very hard and compact. A number of other rock names are applied to varieties of chert. Flint is dark-colored chert that contains organic matter to contribute the dark color. Jasper is a red variety, deriving its color from iron oxide. Chert occurs in banded forms that are commonly called agate.