Chemistry of Diamonds

The word 'diamond' derives from Greek adamao, meaning 'I tame' or 'I subdue' or the related word adamas, which means 'hardest steel' or 'hardest substance'. Everyone knows diamonds are hard and beautiful, but did you know a diamond could be the oldest material you might own? While the rock in which diamonds are found may be 50 to 1,600 million years old, the diamonds themselves are approximately 3.3 billion years old. This discrepancy is because the volcanic magma that solidifies into rock where diamonds are found did not create them, but only transported the diamonds from the Earth's mantle to the surface. Diamonds also may be formed under the high pressures and temperatures at the site of meteorite impacts. The diamonds formed during an impact may be relatively 'young', but some meteorites contain star dust, debris from the death of a star, which may include diamond crystals. One such meteorite is known to contain tiny diamonds over 5 billion years old. These diamonds are older than our solar system!


Start with Carbon

Understanding the chemistry of a diamond requires a basic knowledge of the elementcarbon. A neutral carbon atom has 6 protons and 6 neutrons in its nucleus, balanced by 6 electrons. The electron shell configuration of carbon is 1s22s22p2. Carbon has a valence of 4, since 4 electrons can be accepted to fill the 2p orbital. Diamond is made up of repeating units of carbon atoms joined to four other carbon atoms via the strongest chemical linkage, covalent bonds. Each carbon atom is in a rigid tetrahedral network where it is equidistant from its neighboring carbon atoms. The structural unit of diamond consists of 8 atoms, fundamentally arranged in a cube. This network is very stable and rigid, which is why diamonds are so very hard and have a high melting point.

Virtually all carbon on Earth comes from the stars. Studying the isotopic ratio of the carbon in a diamond makes it possible to trace the history of the carbon. For example, at the...