Common salt crystals. Coloured scanning electron micrograph (SEM) of common, or table, salt (NaCl). These salt crystals are built up from a cubic lattice of sodium and chloride ions. In the absence of impurities an exact cubic crystal form would be produced. In practice, however, this basic cube is usually disrupted by dislocations. This gives rise to crystals with a variety of shapes, although they all retain the basic cubic symmetry. Salt is widely used as a preservative in curing, and also as a flavour enhancer and flavouring. Magnification: x17 when printed 10 centimetres wide.