Diamond

It has hardness of 10 Mohs. It is formed of carbon and its specific gravity is 3.51. 
Unique in the world of gemstones, Diamond is the hardest of all materials. Perhaps it is because of this durability that diamonds are treasured as symbols of devotion and purity. And yet within the structure of Diamonds we often find impurities, or "inclusions," that trap light, distracting our eye from the radiance we so value.

Sometimes these tiny imperfections are removed by cutting them away. Often we employ methods that do not sacrifice precious Diamond in the process. Today we have perfected a fascinating enhancement technique that focuses tiny beams of laser light at imperfections and vaporizes them. The minute passageways created by the laser beam may be filled with clear resins or glass-hard substances, rendering them nearly invisible to the naked eye. Only extreme heat or specifically formulated chemicals remove the filling from the laser passageways. This method is also utilized to fill fissures that reach the stones surface, thereby rendering them less visible to the naked eye.

Diamonds may also be colored in a variety of hues. Fancy colored diamonds are almost as much fun as colored gemstones! Like colored gemstones, each one is different. They come in fabulously expensive pale pinks and blues, pale to bright yellows, oranges, greens, and all those brown colors that are now being called names like cognac and champagne.  Extreme heat and/or irradiation permanently enhance certain natural color properties, allowing them to display their hues in more brilliant range. Whether irradiated, lasered or cut from the mot perfect raw material, your jeweler will inform you of the magical journey your Diamond has followed, from deep within earths mantle to the fine, finished gemstone you have before you.
So, buy a diamond instead of a colored gemstone if you must, but at least consider a fancy colored diamond which will give your jewellery more character, more individuality, more color!