4.50 Ct. Semi-Black Opal from Australia

This specimen is a 4.50 carat Semi Black Opal, presented in a freeform shape with dimensions 17.16 x 12.53 x 3.69 mm, originating from Australia, offered by The Natural Gemstone Company. The piece is translucent, exhibiting a darkened body tone typical of semi black material, which enhances the contrast and saturation of the play of color. The cut is not applicable, because the stone has been worked as a freeform polished gem, rather than a faceted pavilion, the profile shows a gentle dome and smoothly contoured edges that maximize surface area for color play. The polish is graded excellent, producing clean surface reflections and minimal polish haze, this finish allows the internal color flash to be observed cleanly at a variety of viewing angles.

Optical behavior is the defining characteristic of this opal, color intensity is described as intense, with a vibrant display dominated by green and blue spectral components, and with intermittent flashes of violet and red visible at oblique angles. The play of color is broad and patchy rather than a tight pinfire, indicating the presence of a varied silica sphere lattice and localized areas of coherent diffraction, this yields a multi color display that shifts as the stone is rotated. Translucency permits light transmission through the body, producing an inner glow that interacts with the play of color, the semi black body tone deepens the perceived saturation, making the greens and blues appear more vivid against a subdued background. For technical buyers the combination of intense color intensity and translucent body suggests a balance between depth of tone and internal diffraction efficiency, an attribute valued in higher end opal material.

Clarity is graded very slightly included, evaluated at eye level, the inclusions present are primarily subtle linear growth features and narrow healed fissure planes that do not significantly interrupt the play of color, they are visible under close inspection but do not detract from the overall visual performance of the gem. No enhancements have been applied, the stone is natural and untreated, this preservation of original structure is important for long term stability and value, because certain treatments can compromise durability or alter optical characteristics. The excellent polish and careful freeform shaping indicate skilled lapidary work, the cutter has prioritized preservation of play of color and maximization of face up color area, rather than imposing a standardized faceting scheme, this approach is typical for high quality opal nodules where natural color seams dictate orientation and final shape.

From a setting and practical perspective, this freeform Semi Black Opal is ideal for secure bezel mounting or custom fitted settings that shield the edges, because the non faceted profile and relatively thin maximum depth of 3.69 mm require protective mounting to minimize chipping risk. Orientation during setting is critical, the primary color flash banding should be oriented to the viewing plane to maximize face up color, a shallow bezel that follows the contour will preserve the dome and allow light to enter and interact with the internal silica array. Care instructions for the buyer include avoiding thermal shock and harsh chemicals, opal is hydrated silica and can be sensitive to abrupt temperature changes and prolonged exposure to solvents, routine gentle cleaning with mild soap and water and a soft brush is recommended, professional inspection before any extensive setting work is advised to evaluate internal features and to determine the optimal mounting strategy. For clients seeking a distinctive Australian Semi Black Opal with intense play of color and natural, untreated integrity, this 4.50 carat freeform piece from The Natural Gemstone Company represents a technically interesting and visually rewarding option.