Flint (Lead Author: WGT)
Flint is a dense, very hard, siliceous rock which occurs in the Upper Cretaceous White Chalk Sub-Group. Flint is essentially the same as Chert, covered separately in this website. In both cases the silica is biogenic, sourced by sponges and micro-organisms with a silica skeleton. The silica has replaced a host limestone, in this case Chalk.
Flint ranges in colour from white to virtually black (but translucent when thin). There is often a white-pale grey “rind” to nodules of flint where the silica merged with the calcite of the host chalk. In West Dorset the flints tend to be greyer with thicker “rinds” than the more pure grey-black flints from Hants and further east. Flint usually forms as discrete nodules, often replacing (and enlarging) burrow systems (Trace Fossils) made by crustaceans in the chalky sea bed some 90-80 million years ago (Turonian-Campanian). (see photo Right)
Flint nodules used in buildings were often recycled, sourced from alluvial or river terrace gravels in Dorset and can have an orange-stained rind (e.g. cobbles used in Cerne Abbas which come from the Clay-with-Flints on the hill to the east of the village). In East Dorset, the Tertiary London Clay includes several pebble beds which are rounded flints, with the rind worn off. They look like Chesil Beach pebbles and were thought at one time to have been collected from Chesil by the Romans for their road which passes Badbury Rings. However, they were collected from the pebble beds in the London Clay which top both Badbury Rings and High Wood (NT) to the east. The Castle Pit RIGS site at Edmondsham is a gravel pit in these London Clay pebble beds.
Flint was and is widely used for walling as cobbles and as knapped flints, sometimes squared and close-fitting, as fill between stone or brick courses. In recent buildings, sometimes flint in pre-cast blocks are used and some such blocks are artificial. The Prehistoric use of flint for tools and subsequently in weapons is well documented (NB. the Stone Age did not end due to the lack of flint or chert…).
Text and photos WGT Feb.2017