Diamond

Diamond is a native crystalline carbon that is the hardest known mineral. It is usually nearly colorless.
When transparent and free from flaws it is highly valued as a precious stone.
It is also used industrially, especially as an abrasive. Crystallized carbon produced artificially is also called diamond.
The name diamond is derived from the ancient Greek adamas ("invincible").
Their hardness and high dispersion of light make diamonds useful for industrial applications and jewelry.
Diamonds make excellent abrasives, because they can be scratched only by other diamonds, or man-made materials, which also means that they hold a polish extremely well and retain their lustre.
They have been treasured as gemstones since their use as religious icons in ancient India. Thier usage in engraving tools also dates to early human history.
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 marketing campaigns.