Besides natural diamonds, the jewelry market deals with imitations and (lately) with synthetics and treated diamonds. The imitation is any substance that is not diamond but is passed off as diamond (for example, it can be a different mineral, a glass, or a compound not existing in nature, which is grown in the form of a crystal). The synthetic is a man-made diamond grown artificially. Natural and synthetic diamonds have almost identical properties. Finally, there are natural and synthetic diamonds on the market, subjected to special treatment besides cutting. Such diamonds are called treated ones. All these objects have their own cost, but sometimes they are passed off as untreated natural stones. Of course, a gemologist should identify both imitations and synthetics, as well as treated gemstones.

Identification of a gemstone should reveal its sort (name), authenticity, natural or synthetic origin, possible presence of treatment traces. The identification is based on special methods and algorithms and implies using some special instruments and hardware. Each stone has a set of diagnostic features that can be divided into direct and indirect diagnostic features.