Diamond
Because of this, many important industries use diamonds as tools for cutting and polishing things. Many of them are clear, but some of them have colors, like yellow, red, blue, green and pink. Big diamonds are very rare, and are worth a lot of money. This is because a diamond is very useful - it is very hard and it spreads light very well. There are natural and synthetic diamonds. The earth makes natural diamonds. People make synthetic diamonds. Diamonds are the hardest natural substance known to man.