Texture: Very fine-grained and smooth; conchoidal fracture. Rough on weathered surfaces.
Structure: Flint and chert form rounded nodules of widely differing forms, but chert also forms massive beds. Flint nodules are often hollow and may contain a fossil, such as a sponge or echinoid.
Mineralogy : Composed of silica, mainly the variety chalcedony. Some authors distinguish flint and chert compositionally but the differences, if any, are slight.
Field relations: Flint and chert nodules occur typically in limestone and chalk. They are usually patchily distributed but often concentrated along one bedding plane. Their origins are not fully understood; but some appear to be secondary replacements of the host rock, whilst others may represent primary deposition on the sea bed of colloidal silica. (Hamilton et al 1976, 204)
patinated flint