10.50 Ct. Cabochon Boulder Opal from Australia

This listing describes one beautiful opaque 10.50 carat marquise shape multi color opal, a Boulder Opal originating from Australia, presented by The Natural Gemstone Company. The gem measures 34.30 by 8.80 by 4.80 mm and is fashioned with a cabochon cut that emphasizes its surface play of color, with intense color intensity and an excellent polish. The piece is an assembled doublet, a common and accepted enhancement for thin opal slices, in which the opal layer is mounted on a contrasting backing to increase stability and to concentrate the visible color response. The marquise outline and the elongated profile were chosen to showcase directional flashes of color across the stone surface, and the overall presentation is consistent with professional lapidary standards for boulder material, where the ironstone matrix or a manufactured backing provides structural support.

In terms of material structure and optical behavior, this Boulder Opal exhibits the characteristic diffraction based play of color that defines opal, rather than the refractive brilliance associated with faceted gemstones. The cabochon form preserves uninterrupted color fields, allowing broad areas of blue and green to shift and intermix as viewing angle and lighting change. The doublet construction complements this by providing a dark or stable base which increases contrast, making the color appear more saturated and vivid. The excellent polish reduces micro surface scattering, improving definition of the color patches and promoting smooth color transitions. The dimensions and thickness result in a gently domed silhouette with sufficient depth for secure setting, while recognizing that assembled opal layers require thoughtful mounting to avoid stress at the thin margins.

When compared to more common gemstones such as diamond, sapphire, and emerald, the opal’s optical appeal operates through a different mechanism, and this difference is central to why this piece stands out. Diamonds exhibit scintillation and high dispersion because of a high refractive index and faceted geometry that create numerous internal reflections. Sapphires and emeralds derive their visual presence from strong selective absorption that produces stable, single hue saturation. By contrast, the brilliance of this Boulder Opal arises from microscopic silica sphere arrangements that diffract light into multiple spectral colors, producing iridescent flashes that move across the surface. The result is not a static brilliance but a dynamic, living colorplay that can show multiple hues simultaneously, and in this specimen the combination of intense blue and green tonalities with occasional secondary color hints gives a broader chromatic range than many monocolor gems. The marquise cabochon maximizes edge to edge color movement, and the ironstone backing used in the doublet increases apparent depth of color, so that the perceived brightness and saturation of this opal are notably pronounced when viewed in typical jewelry lighting situations.

From a practical and gemological perspective, a few considerations support appropriate selection and care, and help to preserve the qualities that make this Boulder Opal desirable. As a doublet, the item benefits from the color enhancement and structural support of the backing, but the bonded interface and the thinness of the opal slice make it advisable to protect the stone from thermal shock, prolonged immersion in liquids with detergents, and aggressive mechanical impact. Bezel settings or protective mountings that encapsulate the margin are recommended to reduce the risk of lifting or edge chipping, and routine maintenance is best achieved with a soft cloth and mild soapy water applied briefly, followed by careful drying. Ultrasonic cleaners and steam should be avoided with assembled opals. The Natural Gemstone Company provides imagery, measurements, and the origin designation Australia to support accurate appraisal and design decisions, and this specimen is suitable for use in bespoke pendants or rings where the elongated marquise form can be presented flat or slightly raised to emphasize the moving color. The combination of authentic Boulder Opal material, precise cabochon shaping, intense color intensity, excellent polish, and doublet enhancement results in a stone that is both a distinctive optical study and a viable choice for considered jewelry applications.