Carbon 14 dating explained
Most natural diamonds have ages between 1 billion and 3.5 billion years.
Most were formed at depths of 150 to 250 kilometers (93 to 155 mi) in the Earth's mantle, although a few have come from as deep as 800 kilometers (500 mi).
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.
Fresh rock is dark bluish green to greenish gray, but after exposure rapidly turns brown and crumbles.
It is hybrid rock with a chaotic mixture of small minerals and rock fragments (clasts) up to the size of watermelons.
Before the 20th century, most diamonds were found in alluvial deposits.
It is possible that diamonds can form from coal in subduction zones, but diamonds formed in this way are rare, and the carbon source is more likely carbonate rocks and organic carbon in sediments, rather than coal.
Diamond is renowned for its superlative physical qualities, most of which originate from the strong covalent bonding between its atoms.
In particular, it has the highest hardness and thermal conductivity of any bulk material.
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.
Diamonds have been known in India for at least 3,000 years but most likely 6,000 years.