Diamonds are lithologically widely distributed, and are found in unconsolidated and consolidated sediments (placers and paleoplacers), various igneous rock types of deep-seated origin (kimberlite, orangeite, lamproite, alnoite, aillikite, picritic monchiquite, alkali basalt), high pressure mantle xenoliths, high pressure metamorphic rocks, and also meteorites and their impact structures. Of these, only diamond-bearing kimberlite, orangeite, and lamproite, plus associated placers and paleoplacers, are economically viable. Prior to 1960, more than 80% of all diamonds were derived from secondary deposits; by 1990, this figure was less than 25% (Levinson et al., 1992).

Diamond is the only mineral commodity extracted from kimberlite- or lamproite-hosted deposits. Diamonds are subdivided into industrial, near-gem, and gem quality stones. However, they are also described as being either ‘cuttable’ or ‘industrial’ (Levinson et al., 1992). Based on 1992 world production figures, approximately 50% by weight of a total production of 105 Me (where Me = million metric carats; c = metric carat = 0.2 g) was industrial grade, the remainder being cuttable. Industrial grade stones are used for a variety of purposes, but compete with synthetically produced industrial diamonds (estimated 1993 production 450-500 Me; G.T. Austin, pers. comm., 1994).

Only primary diamond deposits are discussed here. These have been subdivided into two groups on the basis of their host rocks, which are either kimberlites or lamproites. In addition to their host rock differences, these deposits also differ in morphology, mineralogy, and other respects. These differences between the two types are discussed in the summary accounts that follow.