Rhenium diboride is a synthetic material with a theoretical hardness comparable to that of diamond. It was first synthesized in 1962 by heating the elements boron and rhenium and mixing them together. In laboratory trials, rhenium diboride has scratched diamond. It belongs in the class of superhard materials.
The class of superhard materials contains substances with high bond covalency and high electron density. These materials possess a hardness value greater than 40 gigapascals and are used in industrial applications involving abrasives. Although there are several other superhard materials of comparable hardness, rhenium diboride is prized because of its relatively low cost of manufacture.