Tortoise shell has long been used as an ornamental gem material for art objects, jewelry, and personal items such as combs and eyeglass frames. Though humans have used tortoise shell for thousands of years, the material reached the height of its popularity during the 18th, 19th, and early 20th centuries. The advent of plastic imitations, as well as the passage of laws protecting sea turtles beginning in the 1970s, have led to a drastic reduction in the amount of tortoise shell in the market. Nevertheless, because older material can still be traded, especially in antique pieces, and because numerous imitations exist, proper identification is still important. This study summarizes the gemological properties of tortoise shell and its imitations. In addition to standard gemological data, the results of several spectroscopic techniques are presented; transmission and specular reflectance infrared spectroscopy were found to be of particular value.
