Synthetic diamond crystals and a method of synthesis

A method of manufacturing a plurality of synthetic diamond crystals, the method including providing a reaction compact comprising a plurality of diamond seed particles dispersed within a matrix comprising a carbon source and catalyst material; in which the combined surface area of the diamond seed particles is at least 0.01 square cm per cubic cm of the reaction compact volume; the method further including subjecting the reaction compact to an ultra-high pressure and high temperature at which the catalyst material is molten and diamond is more thermodynamically stable than the carbon source, for a sufficient period of time to grow the diamond crystals on the diamond seed particles; and treating the reaction compact to recover the diamond crystals. The carbon source may be graphite powder. The catalyst may comprise iron, nickel, cobalt, or manganese, or mixtures thereof. Also claimed is a plurality of diamond crystals made by the process as defined above.