Research

GIA Diamond Research

Why is diamond the ‘king of gems’?

From crowns to engagement rings, diamonds have been a central aspect of many of life’s celebrations and historical milestones. They have been associated with legends and folklore. Diamonds have set record per-carat prices and often reside at the pinnacle of the gem and jewelry world.

Diamond stands at the apex of the hardness scale with a value of 10. It also has the highest thermal conductivity and the highest molar density of any terrestrial material, as well as a high resistance to acids, corrosion, and radiation. This extraordinary combination of physical properties not only makes it ideal for daily wear in jewelry – often through many generations - but has also led to its exploitation for a wide range of industrial and technological applications. Diamond’s remarkable potential has spurred the rapid evolution of laboratory-grown gem-quality diamonds in the last 20 years.

Natural diamond geology/Mining locations

Diamond is mined across the world, with historic deposits found in India and Brazil and major current deposits in Canada, southern Africa, Australia, and Russia. GIA research into geological formation is an important initiative and focus. Diamonds are effective messengers as they preserve and transport inclusions from the deep Earth and thus reveal much about our planet that would be otherwise inaccessible. They are the deepest occurring gemstone on Earth, with most forming at depths of ~150 – 200 km. However, analysis of inclusions in rare large, high-quality diamonds has revealed that they come from greater depths than most diamonds – up to 800 km deep. Diamond formed up to 3.5 billion years ago and were brought up to the surface through ancient volcanic eruptions in a matter of hours, a testament to their resilience!

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Diamonds are effective messengers as they preserve and transport inclusions from the deep Earth and thus reveal much about our planet that would be otherwise inaccessible

Causes of color and optical features

GIA has the unique opportunity to examine some of the rarest fancy-colored diamonds. Though the “classic” diamond may be colorless, natural diamond can occur in almost all colors. It is one of only a few gemstones that is valuable with both saturated color and complete absence of color. However, it most often occurs in yellowish and brownish hues. The color is associated with minute atomic-level lattice irregularities and impurities – scientifically termed “defects” or “optical centers.” The optical centers that contribute to a diamond’s color are important as an understanding of their formation is the scientific basis for the reliable distinction between natural and treated color. GIA published a first-of-its-kind series of articles which discussed in depth the causes of color and the statistics of diamonds across the rainbow.

Colored Diamonds

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Laboratory-grown diamonds

First created in the 1950s, laboratory-grown diamonds have dramatically altered the landscape of the diamond trade. Gem-quality laboratory-grown diamonds can be formed by either the high pressure, high temperature (HPHT) or chemical vapor deposition (CVD) methods. Whether examining the laboratory-grown diamonds submitted for grading reports, growing CVD diamonds at our research facility in New Jersey, or altering these materials through treatments, GIA is staying at the forefront of characterization and identification of laboratory-grown diamond.

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Grading report – related features

GIA is the creator of the 4C’s – the internationally recognized scale of diamond grading. Among the quality factors listed on the report, GIA is consistently researching various aspects of color and cut along with long-wave fluorescence observations.

Advanced Instrumentation

By eye, certain diamonds may seem indistinguishable. GIA uses a wide range of advanced spectroscopic and imaging techniques to evaluate the presence, absence and relative concentrations and distributions of atomic-level lattice irregularities present in all diamonds. Referred to as optical centers, these features provide clues for diamond identification. Below is a snapshot of some of the key instruments used.

Learn more here about our advanced research instumentation.

Photoluminescence (PL) Spectroscopy and Mapping

PL spectroscopy is a vital tool for advanced testing in gemological laboratories as it has the sensitivity to detect optical center concentrations down to parts-per-billion (ppb) levels. Lasers are used to excite characteristic luminescence (emission of light) from defects present in diamonds. The lasers include wavelengths from the UV through the near-IR. Typically the diamonds are cooled to liquid nitrogen temperature (-196^oC). By moving the sample while data are collected, thousands of spectra can be compiled and stitched together, creating a map of defect distributions.

PL with Laser

Visible and Infrared Absorption Spectroscopy

When light passes through a stone, some will be absorbed by optical centers present in diamonds. Absorption in the visible wavelength range can result in color, whereas absorption in the infrared (IR) is invisible. Careful analysis of absorption spectra can reveal the source of color in a diamond and show the presence of common elemental impurities such as nitrogen and boron. IR absorption spectroscopy is the basis for the Diamond Type classification system.

Deep UV Fluorescence Imaging

This instrument uses ultra-shortwave (<230 nm) UV radiation--a lower wavelength and higher energy than the ultraviolet light typically used for fluorescence observations in routine gemological work. Diamonds are strong absorbers of deep UV light, resulting in fluorescence emission of defects present near the sample surface, providing detailed information of their distributions and revealing diamond growth patterns. Additionally, almost all diamonds will show some observable fluorescence to deep UV light, including those that show as “UV fluorescence: None” as the UV fluorescence description on grading reports (based on long-wave UV excitation at 365 nm).

Diamond View

There are several gemological methods that are helpful for diamond identification. While often they may not be diagnostic, they are important tools for gemologists regularly analyzing diamonds.

Screening and gemological instruments

GIA has a long history of developing innovative instruments and gemological tools to aid in diamond characterization, for both internal and external users. Learn more about instruments available for the trade in https://www.gia.edu/instruments.

Photomicroscopy

Photomicroscopy (also known as photomicrography) allows gemologists and scientist to capture high magnification (up to 1000x) digital images of sample features, such as characteristic surface textures or internal inclusions that may be trapped during natural or laboratory-grown diamond formation. Different lighting conditions, such as darkfield, brightfield and polarized light, can be used to enhance features. These photographic records can provide a wealth of information relating to a sample’s origin.

Left image: Sapphires, one of the rarest inclusions encountered in diamond, suggest an eclogitic origin. Field of view 0.99 mm. Right image: Brown stains were observed next to a green one at a trigon on a rough diamond.

Fluorescence

Gemologists often consider diamond fluorescence when exposed to long- (365 nm) or short- (265 nm) wavelengths. Long-wave fluorescence observation (the color and intensity) is also provided on GIA’s grading report. Fluorescence behavior can also be helpful for distinguishing natural from laboratory-grown diamonds. HPHT- and CVD-grown diamonds generally show a stronger fluorescence reaction to short-wave UV than to long-wave UV; in contrast, natural diamonds show a stronger fluorescence reaction to long-wave UV than to short-wave UV. Additionally, HPHT-grown diamonds often show persistent phosphorescence – the emission of light following UV illumination.

GIA iD100^®

Based on decades of research on natural and laboratory-grown diamonds, GIA developed simple screening equipment that the trade and public can use to positively identify natural diamonds and refer any suspicious diamonds that may be laboratory-grown, treated or simulants for further testing. An accurate screening device, the GIA iD100^® automatically collects and analyzes a diamond’s luminescence when illuminated with ultraviolet light. If a natural signature is detected, the sample is passed within a couple of seconds. Otherwise, it is referred, indicating that the sample could potentially be laboratory-grown or a simulant. This allows people, through the simple push of a button, to confirm whether diamonds are natural. Primarily used for the analysis of colorless and near-colorless diamonds, additional functions for pink, green, brown and blue diamonds have also been developed. Learn more about the GIA iD100^® at https://discover.gia.edu/id100. https://youtu.be/sKmMSvdd69w