Chert is a hard, cryptocrystalline silica of sedimentary origin. It is often to be found as nodules & irregular masses within sedimentary rocks. It is specifically associated with chalk & marly limestones. They can be found in variety of colours from dark grey-black, brown, green through to yellow & white. Often with a white, rough textured outer layer. Supplied in lots of 1 kilogram in a polythene bag with data label, size of pieces may vary.
