chalcedony
Chalcedony is the name given to compact varieties of silica which comprise minute quartz crystals with sub-microscopic pores. There are two main varieties: chalcedony, which is uniformly coloured, and agate which is characterised by curved bands or zones of differing colour."​ (Hamilton et al 1976, 130).

It has conchoidal fracture and therefore has the same knapping qualities as flint.
Flint, chert, carnelian, and jasper are all varieties of chalcedony.