Material involved in the present study was supplied through the Diamond Trading Company (London). Samples are referred to throughout the text by numbers prefixed by GU (Guinea) where suffices are adopted according to the methodology described in appendix 3.1.

Guinea has a modest yet significant diamond production. Geologically, it occupies part of the West African Craton which extends into Sierra Leone, famous as the source of the world’s third largest gem diamond (the 969.8 carat ‘Star of Sierra Leone’). Historically, diamonds have been available on the market from suppliers in Conakry, the capital city of Guinea. However, the sources of material on this market are poorly constrained and probably include some illegally imported stones from Sierra Leone. Recently, however, stones have become available from Kankan, a locality inland where the source area is far better constrained (Harris, 1996, personal communication). It is from this supply source that the Guinean diamonds considered herein were obtained.

Archean granitoids and Archean and Proterozoic supracrustal metamorphic rocks form the well exposed basement of this part of the West African craton (cf. Hurley et al., 1971). Kimberlite intrusions are fairly prolific (eg. Rombouts, 1987), but the diamond grade varies considerably. For the Kankan area, Sutherland (1993) presents the characteristics of the kimberlite dykes of the upper drainage basin of the Mandala River (~8°30’N ~9°30’W), figure 1, and their associated alluvial diamond deposits. He describes diamonds under 24 subdivisions, involving floodplain, terrace, pediment and slope from 8 localities. Although no detailed study has been made of the inclusion parageneses from the Mandala basin, the diamond characteristics show striking similarities to features of lower mantle sourced stones from São Luiz and Guinea described in sections 5.1 to 5.3. These similarities, in terms of quantity of plastically deformed, dodecahedral or irregular, pitted, inclusion-rich stones, may not be entirely coincidental. Amongst nearby Guinean sources, there is much variability; some appear to be distinctly different e.g. Benko (Rombouts, 1987), indeed throughout Guinea and Sierra Leone striking variations between very proximal deposits are commonplace; others, however, show strong similarities with Mandala Basin material (Sutherland, D. (Placer Analysis), 1994 personal communication).