17.18 Ct. Multi Color Cabochon Onyx from Madagascar

This translucent multi color onyx presents as a substantial 17.18 carat oval cabochon, precisely measured at 19.49 x 14.44 x 7.29 millimeters, exhibiting a clean, symmetrical outline and an even domed profile that optimizes face up color and internal structure. The cabochon cut is executed to exacting lapidary standards, with a centrally placed apex, calibrated dome curvature to balance light transmission and surface reflection, and a consistent girdle thickness that facilitates secure mounting. The surface retains an excellent polish, achieved through progressive micron grade abrasives, which yields a smooth vitreous to slightly waxy luster appropriate to cryptocrystalline chalcedony. There are no treatments or enhancements, the material is wholly natural, and the piece is sourced from Madagascar, a region noted for producing high quality chalcedony variants with complex color zoning.

From a gemological perspective this onyx sits within the chalcedony group, chemically SiO2, with a refractive index typically near 1.53 to 1.54 and a specific gravity in the region of 2.60 to 2.64, characteristics that confirm its silica based, cryptocrystalline structure. The designation color intensity not applicable reflects the multi tonal nature of the piece rather than a single saturated hue, and under transmitted and reflected light the material displays layered color transitions and subdued internal banding that provide visual depth without strong pleochroism. The absence of macroscopic cleavage combined with the fine interlocking fibrous microstructure contributes to consistent toughness, while the translucent body allows subtle internal patterning to read clearly through the domed surface, enhancing the perceived size and presence of the stone.

Durability attributes make this onyx an excellent candidate for daily wear jewelry, provided appropriate settings and routine care are observed. On the Mohs scale the material registers approximately 6.5 to 7, offering strong resistance to abrasion from many common contacts while remaining softer than corundum and diamond class stones, so care should be taken to avoid scraping against harder materials. The cabochon profile reduces the risk of perimeter chipping relative to faceted sharp edges, and the excellent polish minimizes surface micro abrasions that would otherwise diminish translucency over time. The material is stable to ordinary light exposure and normal thermal conditions encountered in daily use, however it is prudent to avoid prolonged exposure to strong acids and harsh industrial chemicals. For cleaning we recommend warm soapy water and a soft brush, with ultrasonic and steam cleaning reserved for evaluation by a professional when mounting and setting details are known.

For secure everyday mounting a bezel setting is recommended to protect the cabochon rim and distribute impact stress across the girdle, however a well designed prong setting with protective crowns or a partial bezel can also provide both security and maximum face up display. The dimensions and weight of this oval make it particularly suitable for statement rings, pendants, or masculine cufflinks where the substantial face enhances color play and presence. The provenance from Madagascar, coupled with the lack of enhancement, positions this piece as a collectible natural specimen with stable long term performance. The Natural Gemstone Company stands behind the craftsmanship and disclosure of this onyx, and we can provide additional technical documentation or bespoke mounting recommendations to ensure optimal durability and aesthetics for everyday wear.