Gemological Institute Of America | All About Gemstones

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Advanced Gemological Testing

New Gems & Gemology Issue

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Research & News

Figure 6. This selection of deep-UV fluorescence images of natural diamonds highlights the wide range of potential emission patterns and colors that can be observed, evidence of diamond’s unique growth and residence history. E: Most natural type II diamonds show blue fluorescence with mosaic-like polygonized dislocation patterns, differing from characteristic type II CVD- or HPHT-grown diamond patterns (compare with figures 8–10). Images by Garrett Koneval (A), Najmeh Anjomani (B), Wuyi Wang (C), Christopher Vendrell (D), Ulrika F.S. D’Haenens-Johansson (E), and Sandeep Kabariya (F).

Glowing Gems - What Does Fluorescence Tell Us?

G&G in a Flash: What Does Fluorescence Tell Us?

Learn about the principles, mechanisms, and characteristics of luminescence that create the impressive and memorable glow of gemstones.
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CVD diamond plate and HPHT laboratory grown diamond

Laboratory-Grown Diamonds Update

The Latest on Laboratory-Grown Diamonds

Learn the latest trends by GIA on the laboratory-grown diamond industry.
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Hand holding demantoid garnet rough in matrix.

Field Gemology Update

The Latest in Field Gemology from Wim Vertriest

Learn the latest on Madagascar sapphires and demantoid garnets from Wim Vertriest, GIA Manager of Field Gemology.
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Figure 1. Dr. Vince Manson using GIA’s first scanning electron microscope, acquired in 1976.

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Analytical Techniques in Gemology: A Historical Overview

Gemology has become a highly technical field employing analytical instruments for gem testing, driven by the need to address increasingly complex identification challenges in the marketplace.
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Figure B-2. The absorption spectrum of a synthetic ruby measured using a CCD spectrometer is compared to the view in a spectroscope.

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Application of UV-Vis-NIR Spectroscopy to Gemology

UV-Vis-NIR spectroscopy measures how gemstones absorb and interact with light across the ultraviolet, visible, and near-infrared ranges, revealing crucial information about their composition, origin, and potential treatments.
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Figure 9. FTIR spectra for most minerals are distinctive, such as those for diamond and corundum.

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Infrared Spectroscopy and Its Use in Gemology

Infrared spectroscopy, specifically FTIR analysis, measures atomic vibrations to determine identity, cause of color, and potential treatments by analyzing how a gemstone absorbs infrared light.
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Figure 1. Microscope-assisted photoluminescence spectroscopy is an important technique for collecting data in gemological research and identification. Here, a 514 nm laser illuminates a sapphire sample at room temperature, creating red luminescence caused by trace amounts of chromium. Photo by Kevin Schumacher.

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Shining a Light on Gemstone Properties: An Exploration of Photoluminescence Spectroscopy

Photoluminescence spectroscopy examines how gemstones absorb and emit light, uncovering crucial details about their identity and color origin through the detection of microscopic defects and impurities.
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$Figure 10. An old Debye-Scherrer camera formerly used at GIA. A faceted chrome diopside is mounted on a Gandolfi stage that rotates the gem around two intersecting axes to randomize its orientation during data collection. The X-ray beam is directed to the culet of the gemstone by the collimator on the left. A strip of X-ray film lines the inside of the camera to collect the diffraction pattern from the gemstone. The XRD pattern shown in figure 9C was taken using a similar device. Photo by Kevin Schumacher.$

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Raman Spectroscopy and X-Ray Diffraction: Phase Identification of Gem Minerals and Other Species

Raman spectroscopy and XRD techniques are used to identify gemstone species through their atomic-scale structures, with Raman spectroscopy analyzing inelastic light scattering from crystal lattice vibrations and XRD examining X-ray interference patterns from atomic layers.
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Figure A-1. The Horiba Mesa-50 XRF is used by GIA’s laboratories. Gemstones and jewelry pieces can be placed on top of the testing window. A laptop is connected to the testing unit, and the system also has a built-in camera that allows the user to adjust the position of the X-ray beam on the sample. Photo by Kevin Schumacher.

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Chemical Analysis in the Gemological Laboratory: XRF and LA-ICP-MS

The primary chemical analysis methods applied in gemology are XRF, which uses X-ray emissions for nondestructive testing, and LA-ICP-MS, which provides detailed analysis and greater sensitivity. LA-ICP-MS has become essential for origin determination and treatment detection.
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Figure 1. Burmese ruby and diamond necklace and earrings under long-wave ultraviolet illumination, revealing an alluring fluorescence response. Courtesy of a private collector and Mona Lee Nesseth, Custom Estate Jewels. Photo by Robert Weldon.

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Glowing Gems: Fluorescence and Phosphorescence of Diamonds, Colored Stones, and Pearls

Photoluminescence imaging, which analyzes how gemstones glow under ultraviolet light, is an important analytical tool for detecting impurities, natural versus synthetic gems, and treatments through the observation of fluorescence and phosphorescence patterns.
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Figure 9. A section of a multi-strand necklace containing natural saltwater pearls from Pinctada species. Various natural growth structures can be found inside these pearls with X-ray microradiography.

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Applications of X-Ray Radiography and X-Ray Computed Microtomography in Gemology

X-ray imaging techniques revolutionized pearl testing by enabling gemologists to distinguish natural from cultured pearls through detailed visualization of their internal structures, evolving from film-based systems in the early 1900s to today’s sophisticated digital equipment.
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Figure 5. A GIA metrologist uses a calibrated standard to verify instrument performance. Photo by Kevin Schumacher.

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Metrology at GIA

GIA ensures accurate gemological measurements across its global laboratories through rigorous metrology practices, including systematic instrument calibration, validation from traceable standards, and continuous monitoring by trained staff to maintain precision and consistency.
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Figure 1. A red gemstone set table-down in a noncontact optical measurement device. Photo by Annie Haynes.

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Analysis of Gemstones at GIA Laboratories

GIA’s laboratories use advanced instrumentation and research to deliver accurate grading, identification, and origin determination for natural and laboratory-grown diamonds, colored stones, and pearls.
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