Chevron growth refers to a V-shaped or zigzag internal growth structure visible in certain synthetic gemstones, most notably hydrothermal and flux-grown synthetic emeralds and chemical-vapour-deposition (CVD) synthetic diamonds. The pattern arises from fluctuating conditions during crystallisation — variations in temperature, supersaturation, or feedstock supply cause successive growth layers to advance at differing rates or angles, producing the characteristic herringbone or chevron geometry when viewed in cross-section. Because natural crystals rarely replicate these specific growth dynamics, chevron patterning has become one of the more reliable diagnostic criteria for identifying laboratory-grown material.

Formation Mechanism

During hydrothermal synthesis, a nutrient solution is circulated through a sealed autoclave under elevated temperature and pressure. Fluctuations in the thermal gradient — even minor ones — alter the rate at which material is deposited on the seed crystal. When growth accelerates and decelerates cyclically, successive growth zones build up in angular, V-shaped increments rather than the smooth, broadly curved zones typical of natural crystal growth. A similar mechanism operates in flux growth, where changes in the flux melt's composition or temperature produce comparable angular layering. In CVD diamond synthesis, carbon-bearing gas is decomposed over a substrate; variations in gas flow, plasma density, or substrate temperature produce striated layers oriented perpendicular to the growth direction, which manifest as chevron-like banding when the stone is examined under magnification.

Chevron Growth in Synthetic Emerald

Hydrothermal synthetic emeralds — produced commercially by manufacturers including Tairus (Russia/Thailand) and, historically, Lechleitner and Biron — commonly display chevron growth zones when examined under the microscope, particularly with darkfield illumination or immersion. The zones may be accentuated by minute inclusions of flux residue, fine particles, or colouring agents that are preferentially trapped along the advancing growth front. In some specimens the chevron pattern is visible to the naked eye as a subtle angular banding, though in well-cut stones it is more typically a microscopic feature. Flux-grown synthetic emeralds, such as those produced by Gilson, can show related angular growth features, though the precise geometry differs from hydrothermal material. Gems & Gemology has published detailed photomicrographic documentation of these features as part of its ongoing coverage of synthetic emerald identification.

Chevron Growth in CVD Synthetic Diamond

In CVD synthetic diamonds, chevron or striated growth patterns appear as fine parallel to sub-parallel bands running perpendicular to the growth direction — typically the ⟨100⟩ crystallographic axis for standard plate-like CVD growth. Under cross-polarised light, these zones often display anomalous birefringence (strain-related colour banding), and under short-wave ultraviolet illumination they may fluoresce with a characteristic layered pattern. The combination of chevron striations, anomalous birefringence, and the absence of natural inclusion types is considered strongly indicative of CVD origin. Advanced spectroscopic methods — including photoluminescence spectroscopy and infrared absorption — are used alongside microscopic observation by leading gemological laboratories such as the GIA and the Gübelin Gem Lab to confirm CVD synthesis.

Diagnostic Significance

The practical importance of chevron growth lies squarely in gem identification. A gemmologist encountering angular, V-shaped growth zoning in an emerald — particularly when accompanied by nail-head or two-phase inclusions characteristic of hydrothermal synthesis, and in the absence of the three-phase inclusions typical of Colombian natural emeralds — should regard chevron patterning as a strong indicator of synthetic origin. Similarly, in a colourless or near-colourless diamond displaying fine parallel striations and anomalous birefringence without natural graining, chevron structure points toward CVD manufacture. Neither feature is, in isolation, absolutely conclusive; laboratory confirmation using spectroscopy is the accepted standard. Nevertheless, chevron growth remains a front-line microscopic clue that prompts further investigation.

Further Reading

• GIA Gems & Gemology — Hydrothermal Synthetic Emeralds
• GIA Gems & Gemology — CVD Synthetic Diamond