Synthetics & Simulants
Synthetic Versions of Gemstones
If you subscribe to the long held definition of a gemstone being rare, then synthetics cannot even be called gemstones. We call them "synthetic versions".
Synthetics are not new. A. V. Verneuil produced ruby using a flame fusion method in the late 1800's. And that method is still in use today -- although more sophisticated methods produce better synthetics aka "lab" or "created".
Synthetics of a given type have all the same mineral properties of natural gems. That include crystal structure, trace elements that cause color plus the same hardness and durability of their natural counterparts.
But synthetics are lab created and, depending on the type, are produced in mass quantities. They may look pretty, but they are not natural so they are not rare so they are not gemstones, in our opinion.
Synthetics can be extremely beautiful. Bcaue the material is cheap, they are usually cut to near ideal proportion. They are generally flawless to the naked eye.
There is nothing wrong with buying or wearing synthetic ruby, sapphire, spinel, etc -- just as there is nothing wrong with hanging a copy of a Rafael in your living room. But they are not Rafaels nor are they gemstones.
Just be aware that if you have a flame fusion 5 carat synthetic ruby ring, most knowledgeable folks will spot it as a synthetic right away.
A material that is used as a substitute for a gem material, but is of a different chemical composition is a "simulant".
The best example of a simulant might be the substitution of cubic zirconia for diamond.