Abstract Gems & Gemology, Spring 2013, Vol. 49, No. 1

Gemstones and Minerals

Nestled within this huge textbook on analytical archaeometry—an interdisciplinary field representing the interface between the natural and physical sciences and professions such as archaeology, art history, and museum curatorship that uses state-of-the-art technologies to extract structural and compositional information from ancient materials—is a useful chapter for today’s gem professional.

The modern gem trade’s embrace of science, technology, and the information sciences is perhaps best reflected in laboratory testing. Advanced laboratory services are often necessary to detect increasingly sophisticated treatments, and new manmade materials such as CVD-grown synthetic diamonds. Lab testing is also used to detect nanotechnology films for hardness and color enhancement, some sophisticated diffusion processes, and geographic origin, to name a few.

Chapter 10, “Gemstones and Minerals,” is a broad overview of several advanced spectroscopic and imaging techniques used in gemological and university laboratories to meet these modern needs. This 26-page chapter provides the gemologist, jeweler, and appraiser with succinct practical information, using numerous field examples, about advanced testing that can easily be communicated with clients.

The authors recognize that the foundational gemological methods (such as trained observation using magnification/microscopy, refractive index, specific gravity, ultraviolet indications, and optic character) often need to be augmented with advanced lab techniques, especially for conclusive determinations.

UV-visible near-infrared (UV-Vis-NIR) spectroscopy helps identify diamond treatments and determine the geographic origin of certain stones such as tourmaline and emerald. Fourier-transform infrared (FTIR) spectroscopy  helps in the detect of heat treatment in corundum and organic substances used for clarity enhancement, as well as the determination of diamond type. Other applications of FTIR include the separation of natural from synthetic origin in inclusion-free stones and the determination of jade type and treatments. Raman spectroscopy is an important tool in the study of inclusions, the detection of diamond and emerald treatments, and the identification of organic pigments in gems. Energy-dispersive X-ray fluorescence (EDXRF) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) are used in trace-element analyses, determining geographic origin, detecting beryllium treatments, and identify unknown or synthetic materials. Photoluminescence (PL) is applied to the study of natural and treated diamonds as well as pearls, spinel, rubies, and coral. X-ray imaging and radiography are widely used to evaluate cultured and natural pearls, including their treatments.

Abstracted by Edward R. Blomgren