Octagon Cut — The Eight-Sided Outline of the Step-Cut Family
Octagon Cut — The Eight-Sided Outline of the Step-Cut Family
A geometric outline with chamfered corners, most commonly executed as a step cut and used for emeralds, aquamarines, and other elongate crystals
The octagon cut is a gemstone outline with eight straight sides, typically arranged as four longer sides alternating with four shorter chamfered corners. The cut is most commonly executed as a step-cut pavilion with concentric rectangular facets parallel to the girdle, closely related to the emerald cut and to the various rectangular and elongated step-cut variants. The eight-sided perimeter offers practical advantages for brittle materials by removing the vulnerable sharp corners of a four-sided rectangle, while maintaining the architectural, geometric character that the step-cut family is prized for.
Geometry and faceting
An octagon outline can be regular (all eight sides of equal length, as in the perfect octagon) or, more commonly in jewellery, irregular — with four longer sides and four shorter chamfered corners producing an elongated rectangular octagon. The latter form is what is typically meant by octagon cut in trade usage; the regular octagon is occasionally seen but is less suited to the elongate crystal habits of the species most often given the cut.
The faceting beneath the octagonal outline is most often a step cut: rectangular facets parallel to the girdle on both crown and pavilion, descending in concentric rows toward the table on the crown and toward the culet on the pavilion. The step-cut faceting produces the characteristic broad flashes of light, the open table that displays colour clearly, and the architectural geometric appearance associated with emerald cuts. Other faceting arrangements — modified brilliant, mixed cuts — appear occasionally but are less standard.
Why the octagonal outline matters
The chamfered corners of the octagon serve a structural purpose. A perfect rectangle with sharp corners concentrates stress at those corners, making them vulnerable to chipping during setting and wear. The chamfered corners distribute stress more evenly, reducing the risk of damage. For emerald in particular — a relatively brittle gem material with internal fractures — the octagonal outline is materially safer than a rectangular one with sharp corners.
Beyond practicality, the octagonal outline has become aesthetically associated with the step-cut family. The classic emerald cut is, strictly speaking, an octagon cut, with the chamfered corners specified as part of the design. Trade usage often distinguishes emerald cut from octagon cut by length-to-width ratio (emerald cuts being more rectangular, octagon cuts sometimes more square or with proportionally larger chamfered corners), but the overlap between the two terms is substantial and the distinction is not always rigid.
Species commonly cut as octagons
Emerald is the canonical example. The cut originated in part to suit the columnar habit of beryl crystals and to protect the inclusion-fissure-rich material from corner chipping. Aquamarine, morganite, and other beryl varieties are also commonly cut as octagons, drawing on the same crystal-habit and durability considerations. Tourmaline, particularly the elongated colour-zoned varieties, is often cut as an octagon to maximise yield from prismatic rough.
Outside the beryl and tourmaline families, octagon cuts appear in topaz (where crystal habit favours elongate forms), citrine, amethyst, and a range of less common species. Diamonds are occasionally cut as emerald-cut octagons; the related Asscher cut is essentially a square octagon-cut diamond with elaborated step facets.
Length-to-width ratios and proportions
Octagon cuts vary in their length-to-width ratio from approximately 1:1 (square octagon) to 2:1 or longer (elongated rectangular octagon). The choice depends on rough shape, market preference, and aesthetic intent. Square octagons present compact, formal appearance; elongated octagons emphasise the linear character of the step cut and present more dramatically in elongate jewellery designs.
Proportions of crown height, pavilion depth, and table size are governed by the same considerations as in any step cut: too shallow a pavilion produces a window (light leakage through the bottom of the stone), too deep produces extinction (darkening through the centre). Skilled cutters balance these against the material's refractive index and the desired carat weight.