Synthetic nano-polycrystalline diamond (NPD) is one of the latest and most exciting results of scientific efforts to synthesize a mineral that has held the fascination of humankind for ages. Unlike other forms of polycrystalline diamond, it is completely transparent. Owing to the material’s unique structure, it is also much tougher than natural diamond and previous synthetics, either single-crystal or polycrystalline. This represents a significant breakthrough for industrial purposes and for high-pressure research into the nature and properties of minerals, including diamond.