Crystals of Maldon sea salt. The picture shows the crystal structure of an unrefined culinary salt made by evaporation of sea water from the Blackwater estuary, Maldon, UK. The main constituent is sodium chloride, which crystallises with cubic symmetry. Pure sodium chloride crystals often assume the shape of simple cubes, with flat surfaces. The crystals here retain cubic symmetry, including prismatic (centre), but the presence of other minerals gives rise to a rough surface and small shapeless fragments. Maldon salt is prized for its mild flavour, and valued as a finishing salt in cooking. Salt manufacture at Maldon is thought to have begun during the Roman occupation of Britain, and the Domesday book of 1086 mentions 45 salt pans in Essex. Maldon is a favoured site due to the high salinity of the estuary water caused by evaporation from extensive local mud flats. Mag x15 at 10 x 8.