£1.00 – £2.74
Flint, a hard cryptocrystalline silica found as nodules & bands within the Cretaceous Chalk.
Flint, a type of chert, is a hard, cryptocrystalline silica of sedimentary origin. It is often to be found as nodules & irregular masses within sedimentary rocks. Flint is specifically associated with chalk & marly limestones. Whereas common chert occurs in limestones. Flints have a glassy to waxy appearance with a concoidal fracture. 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. The mode of formation is uncertain. It is though that during diagenesis silica in solution migrated to cavities in the host rock where it precipitated. The source of silica could have been the spicules of sponges. Our examples are from the Cretaceous Chalk of Norfolk. Each specimen is supplied in a labelled card tray.