Rock Salt

Large crystals of sodium chloride have a characteristic cubic structure, giving this type of salt its name. Crystallography is the study of crystal structures, which are the regular arrangements of repeating units of atoms or molecules. Each material does not have a unique crystal structure, but there is a standard set of structures that account for most materials. These structures are often named after well-known examples and this is the case with rock salt. The sodium ions and the chlorine ions arrange themselves in a simple cubic array in three dimensions, so that each sodium has six close neighbours of chlorine orthogonally arranged (eg. up, down, left, right, back, front). Similarly each chlorine atom is surrounded by six sodium ions. This is called the rock-salt structure. Other minerals have this structure too, such as potassium chloride, lithium chloride, sodium bromide, and many other halides, oxides and suphides.