“Black Diamond”

A bench jeweller submitted a black stone (Material A) which he claim bought from South Africa, and believed to be a “Black Diamond”. The bench jeweller tested it with his own standard thermal conductivity diamond tester, and the result indicated that the Material A is a Diamond.

The bench jeweller submitted the Material A, and requested us to confirm it as a black diamond.

A standard gemological testing applied on this identification. The Material A measured with result of over-the-limit RI reading under a standard refractometer. Opaque transparency under standard handheld jewellery torchlight, high luster which close to SubMetallic under overhead lighting. Under microscope examination found chipped culet and highly abraded facet edges around the stone. The fracture on culet area shows granular surface, which doesn’t match to the standard diamond step-like fracture, and with the density measured as 3.16 which ruled out the possibility as a diamond which has 3.52 SG.

A standard electrical conductivity tester were used, and the result indicated it as “Moissanite”. The possibility of the Material A is a cubic silicon carbide (3C-SiC), which has density of 3.16, high luster, and high thermal conductivity. Using a standard thermal conductivity diamond tester will mistaken it as diamond.