They are also identical in hardness, luster, and refractive qualities. Because they are made in the lab they are perfect. Imitation gems are not the same chemically as gems that are synthetic or natural. Imitation gems are usually made of glass. Red glass can be made into an imitation ruby.
Green glass can pass as an emerald.
Cubic zirconia is a lab grown gem but it is not the same chemically as it s natural counterpart. Cubic zirconia can be made into a green gem that looks extremely close to an emerald. Cubic zirconia is much cheaper than a natural gem or a gems synthetic counterpart. There is nothing wrong with making synthetic gems and there is nothing illegal about it. But selling or passing off a synthetic gem as a natural gem is illegal and fraudulent.