Some gemstones are manufactured to reproduce other gemstones. For example, cubic zirconia is a synthetic diamond stimulant composed of zirconium oxide. The imitations copy the look and color of the real stone but have neither their chemical nor physical characteristics. Though, true synthetic gemstones are not necessarily imitation. For example, diamonds, ruby, sapphires and emeralds have been manufactured in labs, which possess very nearly identical chemical and physical characteristics to the naturally happening variety. Synthetic corundums, as well as ruby and sapphire, are very common and they cost only a fraction of the natural stones. Smaller synthetic diamonds have been manufactured in huge quantities as industrial abrasives for many years. Recently, larger synthetic diamonds of gemstone quality, especially of the colored variety, have been manufactured.