gems, diamond, imitation diamond, gemology

Gübelin surveys diamond and the principal materials used to imitate it, emphasizing the gemological properties by which natural diamond can be distinguished from simulants. He discusses diagnostic characteristics such as refractive index, dispersion, hardness, specific gravity, luster, thermal behavior, and optical appearance, showing how combinations of relatively simple gemological tests permit reliable separation. The article reflects the increasing variety and quality of diamond imitations available around 1980 and stresses systematic identification rather than reliance on visual appearance alone.