CHERT, n. In mineralogy, a subspecies of rhomboidal quartz; called also hornstone, petrosilex or rock flint. It is less hard than common quartz; its fracture usually dull and splintery, sometimes more or less conchoidal. It is more or less translucent, sometimes at the edges, and sometimes the whole mass, if thin, has the strong translucency of certain horns. Its colors are numerous and usually dull. It is usually amorphous, sometimes globular, or in nodules. It occurs often in veins, especially metallic, in primitive mountains.
Chert is also applied to other minerals besides hornstone. Aikin calls a variety of flint, flinty chert, and the Derbyshire miners apply the term, black chert, to a fusible mineral, whereas the hornstone above described is infusible.
