Diamonds
A diamond is an allotrope of carbon and the hardest known natural material on earth.
It is the third hardest known material after aggregated diamond nanorods and ultra hard fullerite. Its primary uses are in industry and as jewelry. Diamonds make excellent abrasives because they are able to be scratched only with other diamond abrasives.
Approximately 130 million carats are mined annually at a total value of USD $9 billion. About 100,000 kg are synthesized each year.
See also