CHERT, CHERT NODULE

chert, chert nodule: translation

   1. Black, brown or grey rock, consisting of very fine-grained silica, that occurs as horizons of nodules and discontinuous bands, generally less than 200mm thick, within many limestones. It is very hard and almost insoluble in water, so commonly it projects from cave walls where it forms passage or shaft ledges and waterfall lips [9].

   2. Light-cream or gray to black rock composed of silica, found occurring as nodules or layers in limestone, or as a replacement of limestone [10].