Stone Type: Sedimentary
Sediments like sand, silt, and clay are produced by erosion of bedrock outcrops and accumulate in layers on land and under the oceans. The lower parts of these layered deposits become subjected to intense pressure and high temperatures. This compacts the sediments, forces out the water, and minerals such as silica precipitate into the spaces between particles. The particles are cemented together to form sedimentary rock.
Chert
Marine cherts sometimes contain fossils of organisms like diatoms and radiolarians, as well as sponge spicules. Petrified wood is a form of chert where the silica has replaced the structure of the fossil. The internal structure of chert is amorphous and lacks layering, which makes it ideal for stone-flaking. It occurs in a wide variety of colours, and most varieties respond well to heat-treatment to improve the material’s flaking characteristics. Chert is a general category which includes folk classifications like flint, chalcedony, opal, novaculite, porcellanite, and jasper, and many archaeologists prefer to use the folk classifications when describing artefacts.
Flint
The term ‘flint’ is often used interchangeably with chert in popular descriptions of stone tool-making. To further complicate the use of the term, some geologists use ‘flint’ to classify any dark grey to black chert, regardless of whether it derives from chalk deposits. Further, many European-trained archaeologists distinguish chert from flint based on quality, with ‘flint’ referring to the most siliceous variants and more grainy (and usually light-coloured) variants referred to as ‘chert’. Flint that occurs as nodules in chalk is coloured dark or medium grey, black, brown, reddish-brown, or off-white grey.
