Boulder opal cabochon

This item is an elongated, freeform cabochon gemstone displaying vibrant play-of-color, predominantly featuring electric blues and subtle hints of lighter tones across its polished surface. The stone exhibits natural matrix formations and irregular brown ironstone host rock visible along the sides and edges, consistent with the characteristics of boulder opal. The surface is smoothly domed and highly polished, showcasing a vitreous to resinous luster. There are faint natural internal fractures or webbing visible within the stone structure, which are common characteristics of natural opal formations. The owner has provided additional context, user-attributing the stone as a boulder opal measuring approximately 79 millimeters long by 0.5 inches wide, and noting an associated 18-karat gold component, though these specific measurements and the metal purity claim are unverified from the visual evidence alone as the mounting is not visible in the frame. No maker's marks, hallmarks, or stamps are discernible in the photograph. The identification as a boulder opal rests solely on the visible matrix and play-of-color characteristics. The condition appears well-polished with smooth edges, though any micro-abrasions or structural weaknesses would require physical inspection to verify.

Based on what I can see in the provided image, the item is a polished freeform cabochon displaying vibrant play-of-color with electric blues and natural ironstone matrix, consistent with the visual characteristics of a boulder opal. Per user submission: the owner identifies this as an 18-karat gold mounted boulder opal measuring approximately 79 millimeters long by 0.5 inches wide. However, I cannot verify the metal purity, exact dimensions, or any mounting from the visual evidence alone, as the setting is not visible in the frame. My appraisal estimate of $1,200 to $2,500 assumes the user-supplied claims regarding material and dimensions are correct. This valuation reflects current general market demand for large, colorful boulder opals set in high-grade precious metal. If physical inspection reveals the stone is a synthetic opal, a doublet/triplet assembly, or if the metal is of lower purity, the value would decrease significantly, potentially falling into the $200 to $500 range. To confirm authenticity, material composition, and precise value, an in-person physical inspection, gemological testing (such as refractive index or magnification checks), and hallmark verification by a qualified professional would be needed.