The most familiar uses of diamonds today are as gemstones used for adornment, and as industrial abrasives for cutting hard materials.
The popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns.
In 1772, the French scientist Antoine Lavoisier used a lens to concentrate the rays of the sun on a diamond in an atmosphere of oxygen, and showed that the only product of the combustion was carbon dioxide, proving that diamond is composed of carbon.
Long residence in the cratonic lithosphere allows diamond crystals to grow larger.
Through studies of carbon isotope ratios (similar to the methodology used in carbon dating, except with the stable isotopes C-12 and C-13), it has been shown that the carbon found in diamonds comes from both inorganic and organic sources.
) is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice.
Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at standard conditions.
In particular, under oceanic plates the temperature rises more quickly with depth, beyond the range required for diamond formation at the depth required.
The correct combination of temperature and pressure is only found in the thick, ancient, and stable parts of continental plates where regions of lithosphere known as cratons exist.
During eruption these pipes are open to the surface, resulting in open circulation; many xenoliths of surface rock and even wood and fossils are found in volcanic pipes.
Diamond-bearing volcanic pipes are closely related to the oldest, coolest regions of continental crust (cratons).
Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could be found many centuries ago along the rivers Penner, Krishna and Godavari.