Diamonds are minerals that are valued for their durability, beauty, and rarity. They form deep in the earth under conditions of extreme heat and pressure, and are brought to the surface of the earth by the forces of volcanism and weathering. Generally, diamonds - and the rocks they’re found in - are very old. Studying diamonds, therefore, can help scientists reconstruct the processes that were central to the formation of the earth itself.
The physical properties of a diamond are determined more by the crystal structure of the diamond than by its composition - consider that diamond and graphite, despite their vastly different physical properties, are both composed of pure carbon. Every mineral is characterized a particular type of crystalline structure that is largely responsible for its physical properties.