Lab-created/synthetic gemstones have the same physical and chemical properties as natural gemstones, only they are created in a lab environment rather than by nature. The Federal Trade Commission defines lab-created and synthetic gemstones as possessing, "...essentially the same optical, physical and chemical properties as the stone named."
The FTC also requires that lab-created/synthetic gemstones be identified as such by jewelry sellers and also requires that any enhancement treatment your gemstone has received must be fully disclosed, along with any special care requirements. The FTC also regulates how gemstones are advertised and prohibits use of misleading terms and language.
You, the consumer, should know that the terms, lab-created, created, synthetic and cultured, are synonymous and simply mean that the gemstone in question has the same physical and chemical properties as a natural gemstone but is, in fact, man made.
One additional point we'd like to stress is this: A simulated gemstone is NOT the same as a synthetic gemstone. A simulated gemstone mimics the general appearance of a natural gemstone but does not share the gemstone's chemical nor physical properties. A cubic zirconia or even a clear color rhinestone or cut glass, for example, could be loosely considered 'simulated diamond,' mimicking the general appearance of a diamond. A lab-created or synthetic diamond, on the other hand, will share the same physical properties as a natural diamond.
It's interesting to note that, as with natural gemstones, not all synthetic or simulated gemstones are created equal. Lab-created gemstones can and should be judged by the same standards as natural gemstones. Simulated gemstones as well come in a wide range of qualities.
On the high end of simulated diamond materials is Moissanite ®, which was developed by Charles & Colvard of North Carolina (C3). C3's Moissanite® so closely shares natural diamond's characteristics that the Gemological Institute of America noted in its Winter 1997 issue of Gems & Gemology (Synthetic Moissanite: A New Diamond Substitute), that "..The thermal properties of synthetic moissanite are also so close to those of diamond that the thermal probes currently on the market react to synthetic moissanite as if it were 'diamond'."
Moissanite® rates a 9.25 on the Mohs scale, making it slightly less hard than diamond but harder than ruby and sapphire (both of which rate a 9 on the Mohs scale). To confuse matters further, C3's Moissanite® is actually synthetic moissanite. Moissanite (without the registered symbol) is a natural crystal that was first discovered in 1893 and apparently is so rare and discovered in such small quantities that it's simply not viable to use to any degree for commercial jewelry purposes.
Moissanite® first hit the jewelry manufacturing scene in the late 1990's and can now be found readily in fine jewelry, nestled next to both precious and semiprecious gemstones and in settings up to 18k gold or even platinum.
Below are some helpful links if you'd care to read more on the lab-created gemstone topics we've touched on in this page:
GIA abstract: Synthetic Moissanite: A New Diamond Substitute
The Modern Jeweler: Diamonds, Cubic Zirconia and Moissanite: How They Differ