Diamond, a mineral composed of pure carbon. It is the hardest naturally occurring substance known; it is also the most popular gemstone. 

The hardness, brilliance, and sparkle of diamonds make them unsurpassed as gems. In the symbolism of gemstones, the diamond represents steadfast love and is the birthstone for April. Diamond stones are weighed in carats (1 carat = 200 milligrams) and in points (1 point = 0.01 carat). 

A diamond's 4 C's represent the four main components of its beauty and structure: Cut, Color, Clarity and Carat. When looking at a diamond, the eye perceives a balance of its characteristics and components, including, but not limited to, the 4 C's.