A hexagonal cut diamond is a diamond fashioned to present a six-sided polygonal outline, with facet arrangements drawn either from the step-cut family, the brilliant family, or hybrid configurations that blend elements of both. Less prevalent in the trade than the round brilliant, oval, emerald, or cushion cuts, the hexagonal form occupies a distinct niche: it satisfies a demand for geometric precision and architectural clarity that has recurred in jewellery design from the Art Deco period through to the present day. Its regular, symmetrical silhouette — six equal sides meeting at equal angles — gives it an almost crystallographic authority, an aesthetic quality that resonates with the underlying hexagonal symmetry found in certain natural crystal systems, though diamond itself crystallises in the cubic system and is not naturally hexagonal in habit.

Geometry and Proportions

The hexagonal outline is defined by six straight edges of nominally equal length, producing interior angles of 120 degrees at each corner. In practice, cutters work to two broad proportional approaches: the regular hexagon, in which width and length are essentially equal, and the elongated hexagon, in which two opposing sides are extended to produce a form sometimes described as a stretched hexagon or hexagonal lozenge. The elongated variant reads as more directional on the finger and is occasionally confused with a modified emerald cut or a cut-cornered rectangle; the distinction lies in the angled rather than perpendicular corner facets.

Depth percentages and table percentages for hexagonal cuts are not governed by any single industry standard comparable to the GIA's round brilliant cut grading parameters. Cutters must therefore balance table size, crown height, and pavilion depth empirically, using optical modelling software to minimise the risk of windowing — the undesirable transmission of light straight through the stone without internal reflection — which is a particular hazard in step-cut and hybrid step-cut arrangements applied to non-round outlines.

Facet Arrangements

Three principal facet architectures are applied to the hexagonal outline:

• Step cut: Concentric rows of elongated, parallel facets on both crown and pavilion, analogous to the emerald cut. This arrangement emphasises the clarity and colour of the diamond, producing broad, mirror-like flashes rather than the scintillating sparkle of a brilliant. Step-cut hexagons are therefore best suited to stones of high colour and clarity grades, where the open, hall-of-mirrors interior is an asset rather than a liability.
• Modified brilliant: Triangular and kite-shaped facets radiating from a central table or culet, adapted to fill the six-sided outline. The result approximates the light return of a round brilliant while retaining the geometric silhouette. Achieving uniform brightness across six corners — rather than the four of an emerald cut or the curved perimeter of an oval — requires careful adjustment of facet angles, particularly at the acute junctions where two sides meet.
• Hybrid or mixed cut: A step-cut crown combined with a brilliant-cut pavilion, or vice versa. This configuration is increasingly common in bespoke and designer-led production, where the cutter seeks to preserve the graphic linearity of the step-cut table while recovering some of the optical performance associated with brilliant pavilion faceting.

Historical Context

Hexagonal and other geometric fancy cuts gained prominence during the Art Deco period (approximately 1920–1939), when the dominant aesthetic in jewellery, architecture, and the decorative arts favoured rectilinear forms, bold outlines, and the deliberate suppression of organic curves. Platinum's workability and strength allowed jewellers to create open, geometric settings that displayed fancy-cut stones to maximum effect, and the hexagonal outline — with its associations with rational geometry and modernist design — was a natural choice for centre stones and accent elements in the geometric cluster and calibré-cut compositions of the era. Maisons including Cartier and Van Cleef & Arpels produced pieces incorporating hexagonal-cut diamonds and coloured stones during this period, though the hexagonal form was always less common than the baguette, square, and emerald cuts that defined Art Deco diamond cutting.

Interest in the hexagonal cut receded during the mid-twentieth century as the round brilliant reasserted its commercial dominance, but it has experienced a sustained revival since approximately 2010, driven by a broader consumer appetite for non-round fancy cuts and by the influence of independent jewellery designers working in geometric and architectural idioms. The hexagonal cut is now regularly seen as a centre stone in engagement rings, particularly in yellow gold settings that complement its angular character.

Optical Performance and Grading Considerations

Because no standardised cut-grade system exists for hexagonal diamonds, purchasers must rely on visual assessment and, where available, the proportions data reported on a laboratory certificate. The GIA, Gübelin, and other major laboratories will certify hexagonal diamonds for colour, clarity, and carat weight, and will report measurements and proportions, but they do not issue a cut grade equivalent to the GIA's Excellent grade for round brilliants. Buyers should therefore examine the stone in person or via high-resolution video, looking for uniform brightness across all six sectors, the absence of a dark or washed-out window at the centre, and well-defined, crisp facet junctions that confirm precise cutting.

Colour grading of hexagonal step-cut diamonds requires particular attention. The step-cut arrangement concentrates colour in the body of the stone, meaning that a hexagonal step-cut diamond may appear more saturated in colour than a round brilliant of the same GIA colour grade. This effect is analogous to the well-documented colour concentration observed in emerald-cut diamonds relative to round brilliants of equivalent grade, and buyers seeking near-colourless appearances in step-cut hexagonals are generally advised to select stones in the D-to-G colour range.

Setting and Design Applications

The hexagonal outline presents both opportunities and constraints in setting design. Its six straight edges are well suited to bezel settings, which follow the perimeter of the stone cleanly and protect the corners — a practical consideration, since the acute angles of a hexagon are more vulnerable to chipping than the rounded girdle of a brilliant-cut stone. Prong settings are also used, with six prongs placed at alternating corners, though four-prong settings are occasionally employed on elongated hexagons. Halo settings surrounding a hexagonal centre stone with a ring of smaller diamonds or coloured stones have become a popular configuration in contemporary fine jewellery, as the halo amplifies the geometric outline and increases the apparent size of the centre stone.

Hexagonal diamonds are also used as accent stones in cluster and pavé compositions, where their flat, parallel edges allow tight calibré-style setting with minimal metal between stones. In this application they function similarly to baguette cuts, providing a graphic, architectural quality to multi-stone arrangements.

In the Trade

Hexagonal cut diamonds are produced in smaller quantities than round brilliants or the major fancy shapes (oval, pear, marquise, cushion, emerald, radiant, princess), and they are not routinely stocked by diamond wholesalers in the depth of inventory available for those shapes. Bespoke and made-to-order sourcing is therefore common. Rough diamond selection for hexagonal cutting favours flat or macle crystals, which allow the cutter to achieve the shallow depth profile appropriate to a step-cut or hybrid arrangement without excessive weight loss. The yield from rough to polished is variable and depends heavily on the quality and geometry of the starting material.

Pricing benchmarks for hexagonal diamonds are not published in the Rapaport Price List in the same way as for round brilliants and the major fancy shapes, meaning that market pricing is more negotiated and less transparent. Buyers are advised to obtain independent laboratory certification and, where significant expenditure is involved, an independent appraisal from a qualified gemmologist.

Further Reading

• GIA: Diamond Cut — gia.edu
• GIA: Fancy Shape Diamonds — Gems & Gemology