Flint

Flint is a hard, fine-grained form of quartz that occurs as nodules within chalk and limestone deposits, and its use as a building material, called flintwork or flushwork, is a distinctive vernacular masonry tradition of southeastern England and parts of northern France, where suitable stone was scarce but flint nodules were abundant in the region's chalk geology. Builders either laid whole rounded flint nodules within a mortar matrix or knapped them, splitting the flint to expose a flat, glossy black face, and combined the split flints with dressed stone or brick in decorative patterns known as flushwork, seen extensively on medieval East Anglian parish churches. Its extreme hardness makes flint essentially impossible to cut precisely, so it is always used as a random or knapped infill material within a mortar matrix or alongside a more easily worked stone for corners and openings, never alone for load-bearing framing elements.