IGNEOUS ROCKS/Kimberlite 259 Figure 17 The Precambrian cratonic areas of Australia, show ing the location of the Leopold Zone lamproite occurrences and the Argyle diamondiferous pipe (Reproduced from Mitchell RH and Bergman SC (1991) Petrology of Lamproites New York: Plenum Press.) Figure 19 Boars Tusk, a lamproite neck in the Leucite Hills, Wyoming, USA Some Western Australian lamproites form simi lar but less dramatic features (Reproduced from Mitchell RH and Bergman SC (1991) Petrology of Lamproites New York: Plenum Press.) although both are of deep-seated origin, carbonatites occur in and close to rifted geotectonic zones (for example East Africa), characteristically form ring complexes in the underworks of volcanoes (as in the huge eroded Kisingiri volcano in Kenya), and are associated with sodic rather than potassic alkaline igneous suites (intrusive ijolites, melteigites, and jacupirangites carrying nepheline and aegirine, also intrusive uncomopahgrites and turjaites carrying melilite and perovskite, and surface volcanics, nephelinites, and melilitites) See Also Earth: Mantle Gemstones Geochemical Exploration Igneous Processes Igneous Rocks: Carbonatites Shields Volcanoes Further Reading Figure 18 A 58 carat pink cut diamond worth $A38 000 (’ £18 000 sterling) from the Argyle Mine in the Kimberleys lam proite province, Western Australia (photograph supplied by the Western Australian Museum) which they have been mistaken, although the South African occurrences suggest the possibility of a connection Kimberlites and Carbonatites It has been suggested, particularly in Russia, that there is a relationship between kimberlites and carbonatite intrusions and volcanic eruptives, but, Bauer J and Bouska V (1983) A Guide in Colour to Precious and Semi Precious Stones, pp 80 83 London: Octopus Davies RH, Griffin WL, Pearson NL, et al (1999) Dia monds from deep pipe DO 27, Slave Craton, Canada In: Gurney JJ, et al (eds.) The J B Dawson Volume: the P H Nixon Volume, Proceedings of the 7th Inter national Kimberlite Conference April 1998, Cape Town, pp 148 155 Red Roof Design Dawson JB (1980) Kimberlites and Their Xenoliths Berlin, Heidelberg, New York: Springer Verlag Glover JE and Groves DI (eds.) (1980) Kimberlites and Diamonds Nedlands: University of Western Australia, Geology Department and Extension Service Glover JE and Harris PG (eds.) (1985) Kimberlite Occur rence and Origin: A Basis for Conceptual Models in