The Round Cabochon
The Round Cabochon
The default cabochon shape, used for star stones, chatoyant material, and opaque ornamentals
A round cabochon is a cabochon-cut gemstone with a circular girdle outline and a domed top surface. It is the most common cabochon shape in the trade, applied across the broadest range of materials: star sapphire and star ruby, chatoyant chrysoberyl and tiger's-eye, opaque ornamentals such as turquoise and lapis lazuli, and translucent stones where brilliance is not the primary objective. The shape's circularity makes it the natural default for displaying optical phenomena that require a domed surface to project, and its symmetry simplifies setting and matching for jewellery.
Why the cabochon shape
Cabochon cutting predates faceting and remains the appropriate finish for materials whose optical performance does not depend on internal reflection. Three categories of stone require cabochon treatment to display their character. The first is the asteriated and chatoyant group: star sapphire, star ruby, star diopside, cat's-eye chrysoberyl, cat's-eye tourmaline, and similar materials, where parallel needle-like inclusions reflect a band or star of light visible only from a curved surface. The second is the opaque ornamental group: turquoise, lapis lazuli, malachite, sugilite, and others, where the body colour and matrix pattern carry the visual interest. The third is the translucent group, including chrysoprase, fine-grade jade, and certain agates, where a curved dome of suitable depth gives the stone visual depth without the windowing that flat-bottomed faceting would produce.
Round, oval, and cushion are the dominant cabochon outlines. Round is the default for symmetrical phenomena — six-rayed and twelve-rayed stars, axially symmetric cat's-eye effects — and for calibrated commercial work. Oval and cushion are preferred for elongated rough or where the shape better suits the design.
Proportions and optical phenomena
The cabochon's dome height relative to its diameter is the most consequential proportion for phenomenal stones. Asterism in star sapphire and star ruby requires a dome high enough to project the star clearly: a typical fine star stone has a dome height of roughly forty to sixty per cent of the base diameter. Cat's-eye effects in chrysoberyl require a similar high dome, with the cabochon oriented so that the chatoyant band crosses the long axis at the apex. Lower domes — twenty to thirty per cent — are appropriate for opaque material where the dome serves only to give a smoothly polished surface and a comfortable setting profile.
The base of the cabochon is typically flat or slightly concave. A flat base simplifies setting; a concave base lightens the stone and is sometimes used in heavy materials such as hematite. Translucent stones may benefit from a polished base, while opaque stones often have rough or matte bases since the underside is invisible in setting.
Calibration and commercial sizes
Round cabochons are calibrated in standard millimetre sizes for commercial jewellery production, typically from 3 mm through 20 mm in 0.5 mm or 1 mm increments. Standardised sizes allow ready-made findings, mass-produced settings, and machine-set work. Commercial cutters in Idar-Oberstein, Bangkok, Jaipur, and Hong Kong supply the trade with calibrated round cabochons in volume across all common materials.
Non-calibrated, free-form, and one-off cabochons are produced where the rough geometry or the material's quality justifies a custom cut. Fine star sapphires and rare cat's-eye stones are typically cut to optimise the phenomenon rather than to a standard size, and the resulting cabochon is set in a custom mounting.
Material-specific considerations
For corundum (star sapphire and star ruby), the cabochon must be oriented with the c-axis perpendicular to the base of the stone, so that the six-rayed star sits centred on the dome's apex. Misorientation produces an off-centre or partial star and substantially reduces value. Similarly, chrysoberyl cat's-eye must be oriented so that the rutile inclusion plane lies parallel to the base.
For opal, cabochon cutting orients the play-of-colour layer parallel to the dome surface and avoids cutting through into the potch (colourless host material). Cabochon depth must balance the desire to display the colour against the need to retain weight; thin, flat cabochons are preferred where the colour layer is shallow.
For jade, particularly fine jadeite, cabochon cutting is the dominant finish for ring centre stones and pendant pieces. The cabochon's translucency and colour distribution are evaluated face-up; back-lit examination is used to assess internal structure.
In the trade
Round cabochons range from inexpensive calibrated commercial stock at a few dollars per stone to fine star sapphires at five and six figures. The trade evaluates cabochons on shape symmetry, dome proportions appropriate to the material, polish quality, and the strength and centring of any optical phenomenon. For phenomenal stones, the strength and centring of the asterism or chatoyancy is the dominant value driver; for ornamental material, colour saturation and matrix pattern dominate. Round is the most liquid cabochon shape because of its calibration depth and the ready availability of comparison stones at every quality level.