Chert definitions

Webster's 1828 Dictionary

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.

WordNet (r) 3.0 (2005)

n
1: variety of silica containing microcrystalline quartz

Merriam Webster's

noun Etymology: origin unknown Date: 1679 a rock resembling flint and consisting essentially of a large amount of fibrous chalcedony with smaller amounts of cryptocrystalline quartz and amorphous silica • cherty adjective

Oxford Reference Dictionary

n. a flintlike form of quartz composed of chalcedony. Derivatives: cherty adj. Etymology: 17th c.: orig. unkn.

Webster's 1913 Dictionary

Chert Chert, n. [Ir. ceart stone, perh. akin to E. crag.] (Min.) An impure, massive, flintlike quartz or hornstone, of a dull color.

Webster's 1913 Dictionary

Hornstone Horn"stone`, n. (Min.) A siliceous stone, a variety of quartz, closely resembling flint, but more brittle; -- called also chert.

Soule's Dictionary of English Synonyms

n. Hornstone, rock-flint, petrosilex.