An imitation is an object or gemstone which is used to mimic a more valuable object or gemstone. Many synthetic and natural minerals are used to mimic – for example – diamond. Another word for imitation is simulant. There is an essential difference between the use of synthetic and imitation; a synthetic substance is an artificial material which has the same optical and physical properties as the material, while an imitation just merely is a look-a-like. Synthetics may be classified as an imitation when portrayed as a different material.

Imitation jewelry is usually costume jewelry of relatively inexpensive materials. Sometimes these can be of precious metals set with high-quality synthetic gemstones for daily wear while the original, more valuable, items remain in the safe. Some jewelers put the latter type in their showcases to reduce the financial risk after a robbery, or to discourage potential felonious thoughts.