Chert

right|thumb|A piece of flint long, weighing 171 grams

Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a chemical precipitate or a diagenetic replacement, as in petrified wood. Where chert occurs in chalk or marl, it is usually called flint.

distinctive layered units of iron-rich sedimentary rock that are almost always of Precambrian age

early Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness

thumb|Outcrop of Franciscan Assemblage|Franciscan radiolarian chert in [[San Francisco, California ]] thumb|Radiolarian chert outcrop near Cambria, California. Individual beds range from about 2 to 5 cm thick thumb|Radiolarite (Jurassic) from the [[Alps.]] Radiolarite is a siliceous, comparatively hard, fine-grained, chert-like, and homogeneous sedimentary rock that is composed predominantly of the microscopic remains of radiolarians. This term is also used for indurated radiolarian oozes and sometimes as a synonym of radiolarian earth. However, radiolarian earth is typically regarded by Earth

thumb|240px|Spongolite texture, click to enlarge (2MB)

thumb|Jaspilite sample from Minas Gerais, Brazil

thumb|right|Porcellanite from the Czech Republic

biogenic pelagic sediment located on the deep ocean floor

mayan archaeological artifact

thumb|right|240px|Novaculite forms light grey Flatiron (geomorphology)|flatirons in the [[Marathon Uplift area of Texas. ]]