Internal growth and dissolution features are visual characteristics of some natural, synthetic, and treated gem materials. Open channels or need-like structures are occasionally observed in natural diamond, synthetic moissanite (SiC-6H), and chemically-etched synthetic colorless quartz. The distinguishing features among the channel structures in these materials are compared, and possible formation mechanisms of the channels associated with dislocations or dislocation bundles are discussed.
Various non-destructive optical characterization techniques have been used to characterize and identify synthetic gem materials grown from hydrothermal solutions, to include ruby, sapphire, emerald, amethyst and ametrine (amethyst-citrine), from their natural counterparts. The ability to observe internal features, such as inclusions, dislocations, twins, color bands, and growth zoning in gem materials is strongly dependent on the observation techniques and conditions, since faceted gemstones have many polished surfaces which can reflect and scatter light in various directions which can make observation difficult. However, diagnostic gemological properties of these faceted synthetic gem materials can be obtained by choosing effective optical characterization methods, and by modifying optical instruments. Examples of some of the distinctive features of synthetic amethyst, ametrine, pink quartz, ruby and emerald are presented to illustrate means of optical characterization of gemstones. The ability to observe defects by light scattering techniques is discussed.
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