By contrast, imitation stones look like natural stones in appearance only, and may be glass, plastic, or less costly stones. Synthetic gemstones and imitation gemstones should be clearly identified as such.

Laboratory grown synthetic gemstones have essentially the same appearance and optical, physical, and chemical properties as the natural material that they represent. Synthetic gemstones produced in the United States include alexandrite, coral, diamond, emerald, garnet, lapis lazuli, quartz, ruby, sapphire, spinel, and turquoise.

 Laboratory grown simulants have an appearance similar to that of a natural gemstone but have different optical, physical, and chemical properties. The gemstone simulants produced in the United States include coral, cubic zirconia, lapis lazuli, malachite, and turquoise. Additionally, certain colors of synthetic sapphire and spinel, used to represent other gemstones, would be classed as simulants. Colored and colorless varieties of cubic zirconia are the major simulants produced.  In the past few years, the use and consumer acceptance of synthetic and simulant gemstones have grown. Much of this growth is the direct result of the recognition of these gemstones for their own merits, not just as inexpensive substitutes for natural gemstones.