The Halides are relatively simple salts, of which the best known is common Salt (Halite). They consist of a halogen such as Fluorine (F), Chlorine (Cl), and the much rarer Bromine (Br) and Iodine (I) combined with an alkali metal. The halogens are present as large negatively charged cations linked with a pure ionic bond to a small metal positive cation such as Sodium (Na) or Calcium (Ca). The ions behave like almost perfect spheres and consequenlty adopt the highest possible packing configuration, called Close Cubic Packing. Many of these minerals therefore have cubic crystal structures.

Halides are generally soft minerals, many of them soluble in water and many are very important economically. Because of their solubility, most Halides are found in environments associated with water. For example in deposits of hydrothermal origin, near hot springs, and most commonly, in evaporite deposits. However the high solubility means that often the minerals are often washed away when the local aqueous environment changes. Consequently many species are transient and therefore very rare. Even so, some like Halite are so abundant that they are common despite their solublity.

Occasionally Halide minerals may be confused with nitrates and sulphates. However the cubic crystal structure normally sets them apart.

The Halides are divided into the following groups:

• Halite Group - includes halides with the structure of Halite. In Halite NaCl, the Na+ ion is so large, in comparison to Cl-, that it must be surrounded by six halide ions to shield it from other positive Na ions. Each Cl- is likewise surrounded by six Na+ ions, balancing out the electric charge. The resulting arrangement is cubic with identical atoms at the corners of a cube and at the centres of all six faces. In all three axial directions are rows of alternating Na+ and Cl- ions. The halides containing Na (Halite) and K (Sylvite) are very ionic and highly soluble in water. Other halides, like those containing Ag (Cerargyrite) are more covalent and are thus largely insoluble.
• Fluorite Group - includes Fluorite and other minerals with various other metals including Yttrium and Caesium. Because the Calcium ion in Fluorite is divalent (Ca2+) each must combine with two fluorite ions F- in the crystal lattice. Thus eight fluorite ions are needed to shield the each positive metal (Ca) ion from other metal ions. Each fluorine ion, on the other hand, is surronded by four Ca ions. This gives rise to a more complex arrangement than the Halite group, consisting of an octahedral arrangement of atoms. Neverthelss the minerals mostly crystallise in the cubic system, although octahedral crystals are also very common.