chert (chert)

[Cf. E. dial. (Kentish) chart, common rough ground overrun with shrubs; charty, churty, = cherty, rough or rocky; Sw. dial. kart, a pebble. Prob. of Celtic origin: cf. Ir. ceart, a pebble, carrach, rocky, Gael. carr, a shelf of rock, W. careg, a stone: see cars, cairn, and crag1.] A cryptocrystalline variety of quartz, also called hornstone, petrosilex, or rock- flint. It is le hard than quartz crystal, has usually a conchoidal or slightly splintery fracture, is commonly gray-brown or black in color, and is often somewhat translucent. It frequently occurs layers or cretiotrans modules, especially in limestone rocks. The name is also applied to any impure flinty rock, including the jaspers.