Kimberlite, as originally described by Lewis (1887, see Dawson, 1980) was a serpentinized, ultrabasic, phlogopite-bearing, diamondiferous volcanic breccia found at the Kimberley diamond mine, S Africa. The term blue ground refers to unoxidized slate-blue or blue-green kimberlite that occurs below the superficial oxidized zone.
Since its original description, “kimberlite” has been extended to nonbrecciated rocks of similar mineralogy to that from the type locality but lacking diamond, and also to others that, although petrographically different from Kimberley Mine kimberlite, do contain diamonds. Indeed, Wagner (1914, see Dawson, 1980) described two distinct types of kimberlite—“basaltic” and lamprophyric varieties. Although it is now appreciated that textural differences may be due to different modes of emplacement (Dawson and Hawthorne, 1970, see Dawson, 1980), the presence or absence of distinctive phases, together with wide ranges in the proportions of other phases, suggest that...