17.18 Ct. Cabochon Onyx from Madagascar

This specimen is a single, translucent 17.18 carat oval multi color onyx, carefully proportioned at 19.49 by 14.44 by 7.29 millimeters, executed in a classic cabochon profile. As a variety of banded chalcedony, this onyx exhibits the characteristic parallel layering that defines the material, and its translucency allows internal light transmission that enhances the visibility of each distinct color band. The cabochon cut was selected to amplify the stone s natural stratification, with a medium high dome that measures 7.29 millimeters in depth, providing sufficient body to appreciate internal depth while maintaining comfortable wearability for rings and pendants. Color intensity is graded as intense, with well saturated tones ranging from deep black bands to ivory white and warm brown strata, and the polish has been executed to an excellent finish, yielding a smooth, reflective surface without surface pits or lap lines. There has been no treatment or enhancement applied to this piece, and its origin is Madagascar, a locality known for producing banded chalcedony with strong contrast and appealing color variation.

From a lapidary perspective, the craftsmanship is focused on orientation and polish to reveal the most compelling aspects of the banding. The cutter oriented the stone so that the bands run transversely across the face of the oval, creating a bold graphic effect that reads well at multiple viewing distances. The cabochon faceting sequence involved precise preforming to establish symmetry of the outline, progressive smoothing to eliminate preform tool marks, and fine lapping to reach a mirror like polish that maximizes surface reflection without obscuring the internal layering. The dome profile is balanced, avoiding an overly flat or overly steep curvature, which allows controlled surface reflections and internal glow without causing optical distortion. Because onyx is a microcrystalline form of silica with a refractive index around 1.53 to 1.55 and a hardness of approximately 6.5 to 7 on the Mohs scale, the material responds well to high polish, and this example takes a particularly high sheen that enhances contrast between the opaque and translucent bands.

When comparing the perceived brilliance of this multi color onyx to more commonly encountered faceted gemstones, it is important to distinguish between faceted brilliance and cabochon luster. Faceted gemstones such as diamond, sapphire, and topaz rely on high refractive index contrast and precision faceting to produce scintillation, fire, and brilliance, phenomena that arise from dispersion and internal reflection within transparent material. Onyx, by contrast, is typically displayed in cabochon form to emphasize color, pattern, and translucency rather than faceted sparkle. The visual impact of this onyx does not depend on refractive index driven brilliance, but on depth, contrast, and directional light scattering. When illuminated, light enters the translucent bands and is softly scattered by the microcrystalline structure, producing a subtle internal glow and a silky sheen on the dome surface. This effect yields a different but equally compelling presence, one of layered depth and graphic banding, that stands out in settings where bold contrast and organic patterning are desirable. For collectors and designers who value originality and surface intimacy over faceted flash, this Madagascar onyx offers an aesthetic that gemstones such as amethyst or citrine cannot replicate, because the layered architecture presents a visual topography that reads as landscape like, with band width, tone gradation, and edge crispness all contributing to a unique visual signature.

For practical considerations, this onyx is robust enough for a statement ring or an artisan pendant, provided common sense care is observed to protect the polished surface from sharp blows and abrasive chemicals. The absence of enhancement ensures long term stability of color and pattern, and the Madagascar origin adds provenance that many connoisseurs appreciate. At The Natural Gemstone Company we select cabochons with an emphasis on optical orientation and polish quality, and this 17.18 carat oval multi color onyx exemplifies that approach, combining precise cutting, intense natural color, and an excellent polish to produce a stone that performs as a focal element in bespoke jewelry. If you require additional measurements, setting recommendations, or bespoke mounting options, we can provide technical guidance to integrate this piece into a design that preserves the stone s visual axis and maximizes its striking banded contrast.