CVD diamond chevrons are distinctive V-shaped or angular growth banding features observed in diamonds produced by chemical vapour deposition (CVD). Formed parallel to the crystal growth direction during layer-by-layer deposition, these structures arise from periodic variations in growth rate, plasma chemistry, or gas composition within the reactor chamber. They represent one of the most reliable internal indicators used by gemmological laboratories to confirm CVD synthetic origin, distinguishing such stones from both natural diamonds and those grown by high-pressure, high-temperature (HPHT) synthesis.

Formation and Appearance

CVD diamond growth proceeds along the [001] crystallographic direction, with successive carbon-rich layers building up on a seed plate. Fluctuations in the deposition environment — including subtle shifts in methane-to-hydrogen ratios, reactor pressure, or substrate temperature — produce alternating zones of slightly differing crystal perfection or nitrogen incorporation. These zones manifest as the characteristic chevron or herringbone pattern when the stone is examined under appropriate conditions.

The chevrons are typically most visible when the diamond is oriented table-down and examined through crossed polarisers, which reveal strain-related birefringence associated with the growth banding. Under standard magnification, the features may appear as faint, parallel, V-shaped striations or as more pronounced angular bands depending on the growth conditions employed. In some stones the pattern is subtle enough to require careful orientation and lighting; in others it is immediately conspicuous.

Diagnostic Significance

Gemmological laboratories, including the GIA, document CVD chevron patterns as part of the suite of features used to separate CVD synthetics from natural diamonds and HPHT-grown material. Natural diamonds do not exhibit this form of planar growth banding; HPHT synthetics instead display hourglass or sector-zoned growth patterns consistent with their cubic or cubo-octahedral growth morphology. The chevron structure is therefore considered a positive indicator of CVD origin rather than merely a supportive one.

Additional CVD indicators that laboratories assess alongside chevron banding include:

• Graining or strain patterns visible under crossed polarisers, often described as tatami-like or anomalous double refraction
• Strong orange fluorescence under short-wave ultraviolet radiation in some specimens
• Weak or absent fluorescence under long-wave ultraviolet, contrasting with the blue fluorescence common in many natural diamonds
• Characteristic infrared absorption features associated with single-substitutional nitrogen or silicon-vacancy centres
• Absence of natural inclusions such as mineral crystals, clouds, or feathers

No single feature is relied upon in isolation; the chevron pattern forms part of a holistic assessment, but its presence is considered strongly probative.

Post-Growth Treatments

CVD diamonds are frequently subjected to HPHT annealing after growth to reduce or eliminate brown colour caused by vacancy-related defects introduced during deposition. This treatment can alter the visibility of chevron banding: in some cases annealing partially obscures the pattern, while in others it remains clearly discernible. Laboratories are trained to search for residual chevron structure even in treated CVD stones, and the combination of HPHT-annealing indicators with any surviving growth banding assists in identifying the dual-process history of such material.

In the Trade

As CVD diamond production has scaled considerably since the early 2010s, the reliable detection of CVD origin has become a routine concern for laboratories and dealers handling melee and larger stones alike. The chevron growth feature, documented in peer-reviewed gemmological literature including Gems & Gemology, underpins the laboratory protocols that allow grading reports to carry a synthetic origin disclosure. Buyers and traders relying on laboratory certification from accredited institutions can therefore be confident that chevron analysis forms part of the screening process applied to submitted stones.