M-carbon engagement rings, get'em while they're cold!
Diamonds are not the only form of carbon created using high pressure. A team of physicists at Yale University found that graphite, another form of carbon, becomes diamond-like under cold-compression to form a new product called M-carbon.
Under normal circumstances, graphite and diamond are opposites. Graphite is soft and used in electronics because it conducts electricity. Diamond is hard and acts as an insulator. But compressing graphene at 80°F to approximately 200,000 times atmospheric pressure (15 GPa), it takes on a similar strength as diamond but keeps its conductivity. For comparison, synthetic diamond can be made using high pressures of just 50,000 times atmospheric pressure, but at 2732°F. M-carbon is extremely incompressible and hard, to the point where it could even damage diamond.
These images show damaged diamonds used in a diamond anvil cell (DAC) high-pressure gauge. The gauge used two opposing diamonds to compress a sample of M-carbon. (a) M-carbon loaded at ambient pressure. (b) Minor scratch on the anvil surface by M-carbon after reaching a maximum pressure of 32 gigapascals (GPa). (c) Severely damaged anvil surface by M-carbon after reaching a maximum pressure of 50 GPa.
More information: http://www.nature.com/srep/2012/120628/srep00471/full/srep00471.html