Synthetic gemstone are not imitations of real gems, but the actual formation by artificial means of the real precious stone, so that the product is identical, chemically, physically and optically, with the one found in nature. Diamonds, ruby, sapphires and emeralds have been manufactured in labs, which possess very nearly identical chemical and physical characteristics to the genuine article. Synthetic corundums, including ruby and sapphire, are very common and they cost only a fraction of the natural stones.