In simple word, diamond is carbon. A solid form of carbon with the highest hardness of any natural material on earth. Most natural diamonds are between 1 billion and 3.5 billion years. But only 20% of all diamonds can be used for jewelry, the remaining 80% are used in industry.
Color: Colorless, yellow, brown, green, blue, reddish, black
Hardness: 10 Mohs
Specific Gravity: 3.47 - 3.55
Refractive Index: 2.417 - 2.419
How valuable is my diamond?
You'd probably have heard about "4 Cs", they are: color, clarity, cut, and carat (weight). The value of your diamond is measured against these Cs.
The Gemological Institute of America (GIA), has a system of color grading using letters starting at D. The highest quality color grades are D, E, and F.
A clarity grading system also has been devised by GIA. They are: Flawless (F), Very Very Slightly Imperfect (VVSI), Very Slightly Imperfect (VSI), Slightly Imperfect (SI), and Imperfect (I).