Abstract: The invention provides elongate synthetic RD diamond particles, each particle having a long axis and a short transverse axis, the ratio of the long axis to the short axis being at least 3 to 1. Each particle generally has a rib bed structure down its long axis, the ribs of the structure being traces of {111} crystallographic planes and the long axis providing a backbone for the structure and being in the direction <100> crystallographic direction. The invention further provides a resin bond grinding wheel in which these particles are radially oriented. The particles may be made by providing a body of solvent metal in contact with a body of carbonaceous material in a reaction zone, producing zones of the weakness in the carbonaceous body and subjecting the contents of the zone to conditions of pressure and temperature suitable for RD diamond growth so causing the solvent metal to penetrate the zones of weakness and produce the particles.