Imitation, or simulated, stones may at first appear like the real thing, but that's where the similarity ends. They do not share physical character with natural or synthetic stones. Many are made of glass or plastic and most can be detected without difficulty by a jeweller. Moissanite is a newer diamond substitute that's even fooling the pros.
A synthetic stone shares a natural stone's physical, chemical, and optical qualities. The difference? Synthetics are created in a lab. They've been around for a long time, but modern technology allows us to cultivate stones that are difficult to differentiate from their natural counterparts. Ask for a lab certificate to verify authenticity before paying top dollar for a stone represented as natural.