Laboratory-grown diamonds (LGDs) are synthesized using two primary methods: High-Pressure/High-Temperature (HPHT) or Chemical Vapor Deposition (CVD). These methods replicate the earth’s natural diamond-forming conditions. Because LGDs share the exact same crystal structure and chemical composition as mined diamonds, they are chemically and optically identical to their natural counterparts. Despite this similarity, a trained gemologist can definitively distinguish LGDs from natural stones using specialized knowledge and equipment.
Basic Gemological Examination and Limitations
A gemologist begins the identification process with standard equipment, such as a 10x magnification loupe or microscope. Initial examinations focus on the diamond’s clarity, color, and cut, the same parameters used for grading natural diamonds. However, these traditional tools are insufficient for definitive identification because LGDs are real diamonds. They possess the same refractive index, hardness, and thermal properties as natural diamonds, making simple testers or visual inspection unreliable.
LGDs often exhibit extremely high clarity and color grades, sometimes lacking the mineral inclusions typical of mined stones. Gemologists cannot rely on measuring properties like thermal conductivity or refractive index, as these values are identical regardless of origin. Therefore, the basic gemological toolkit can only raise suspicion; it cannot provide conclusive proof of a diamond’s origin. The gemologist must look for subtle, specific markers that reveal the stone’s growth history.
Physical Differences in Lab Grown Diamonds
The key to visual identification lies in recognizing the distinct internal growth patterns created by the two synthesis methods. Natural diamonds grow in an octahedral structure, whereas HPHT diamonds often exhibit a cuboctahedral morphology. This morphology leads to characteristic geometric color zoning when viewed under magnification. CVD diamonds, conversely, are grown layer-by-layer, which results in parallel growth striations or banding that differs significantly from the growth structure of a natural stone.
Another important diagnostic feature is the type of inclusion found within the stone. HPHT diamonds are grown using a metallic flux, and tiny remnants (often iron, nickel, or cobalt) can become trapped inside. These metallic inclusions appear as small, dark, irregular spots and may even be magnetic, a tell-tale sign not found in natural diamonds. CVD diamonds, grown from a carbon-rich gas, do not contain metallic flux, but may instead show tiny, non-metallic dark carbon or graphite inclusions.
The diamond’s reaction to ultraviolet light provides strong clues about its origin. Natural diamonds typically show blue fluorescence, but LGDs often display unusual fluorescence or phosphorescence reactions. HPHT diamonds can exhibit a distinct cross-shaped or banded pattern, while CVD diamonds sometimes show a strong yellow or orange phosphorescence after the UV light source is removed. These subtle visual markers, combined with distinctive internal strain patterns caused by rapid growth, enable a professional to suspect a stone is laboratory-grown before advanced testing.
Specialized Equipment and Definitive Testing
When visual evidence is inconclusive, gemologists rely on advanced spectroscopic equipment to confirm the diamond’s identity. These specialized instruments analyze the diamond’s reaction to light at a molecular level, detecting trace elements and lattice defects that mark the growth process. UV/Visible and Infrared (FTIR) spectroscopy are used to determine the diamond’s type, as many LGDs are Type IIa (containing virtually no measurable nitrogen) or Type Ib (common for HPHT stones).
Photoluminescence spectroscopy is especially effective, as it detects characteristic defect centers introduced during synthesis. The presence and arrangement of specific nitrogen- or silicon-vacancy centers provide a spectral fingerprint unique to either HPHT or CVD growth. Devices like the GIA iD100 utilize this highly sensitive technology to quickly and accurately screen diamonds for their origin.
Specialized imaging systems, such as the DiamondView, use shortwave UV light to reveal distinctive growth patterns often invisible under a standard microscope. These systems make the characteristic geometric zoning of HPHT or the layered striations of CVD diamonds clearly visible. By combining this advanced technology with trained observation, gemologists can confidently distinguish laboratory-grown diamonds from those formed naturally within the earth.