What is the difference between a synthetic gemstone and a simulated or imitation gemstone? 

A synthetic gemstone possesses the same chemical, optical and physical properties as its natural counterpart whereas a simulated gemstone just looks like the stone it is imitating but does not share its properties.

So, what does that mean? In the photo are two blue stones – the one on the left is a synthetic sapphire while the one on the right is blue glass. To the casual observer they are both blue gemstones but there are differences – the synthetic sapphire has the same hardness, lustre, durability and refractive index (RI) as a natural sapphire while the blue glass is glass and therefore possesses the hardness, lustre, durability and RI of glass.

These differences, among others, allow gemmologists to identify whether the blue stone in front of them is a natural mined sapphire, a natural but treated sapphire, a synthetic sapphire, a piece of glass or even a kyanite…

They also have implications for jewellers and their customers – while blue glass may, superficially, look like a sapphire it will not be as durable and will shows signs of wear before a sapphire (whether natural or synthetic). There are also cost implications because glass is cheap, a kyanite will be more expensive, a treated sapphire will be more expensive than that and a natural, untreated sapphire will be more expensive again.