ABSTRACT
Particular types of chert have been given specific names: flint is a very fine-grained, mostly black nodular chert common in Cretaceous chalks; jasper is a red chert, the colouration due to finely disseminated hematite; black chert is a dark-coloured, organic-rich variety that may occur in both bedded and nodular form. Impure cherts, where there is a significant or even dominant admixture of clays or carbonate, are referred to as siliceous mudstones and siliceous limestones respectively.
