Feature Gems & Gemology, Spring 1991, Vol. 27, No. 1

Age, Origin, and Emplacement of Diamonds: Scientific Advances in the Last Decade

Scientific advances in the past decade have completely altered our understanding of certain concepts relating to the age and origin of diamonds. As a generalization, most diamonds formed more than 990 million years ago, deep within the earth, from either of two rock types, peridotite and eclogite. They were stored below the base of cratons for varying periods of time, some as long as 3,200 million years, before being transported to the surface. Kimberlite and lamproite, the two rock types usually associated with diamonds, are only the mechanisms that brought diamonds to the surface and are in no way related to the formation of most diamonds. Other topics that are somewhat more speculative, for example, the source of carbon for the crystallization of diamonds and the mechanism of kimberlite and lamproite emplacement, are also discussed and the latest concepts presented.