This is an optical photomicrograph of a sulfide- inclusion-bearing rough diamond from the Jwaneng Mine, Botswana. Below the natural diamond growth surface, at center, is a hexagonal grain of iron sulfide (Fe-S) surrounded by an irregular black rim. This rim is caused by internal fracture of the diamond on its 150-km ascent to the Earth’s surface in the explosive volcanism of the kimberlitic magma. Sulfide grains like these are removed for rhenium-osmium isotopic analysis to reveal the age of the diamond and the composition of the sulfide. The diameters of these sulfide grains are about 300 microns.

(Image courtesy J.W. Harris; click for larger, higher-resolution copy [390kb])

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