0.51 Ct. Bi Color Sapphire from Thailand

This transparent 0.51 carat oval bi color sapphire measures 5.01 x 4.14 x 2.62 mm, and it is presented in a mixed brilliant cut with an excellent polish. The clarity is graded as very slightly included at eye level, and the color intensity is medium intense. The stone is untreated, with no enhancement recorded, and its origin is Thailand. The oval outline and the balanced proportions deliver a pleasing table and girdle relationship that supports even light distribution, while the mixed brilliant cut combines a faceted crown with a finely faceted pavilion to optimize both light return and scintillation. This sapphire is offered by The Natural Sapphire Company, and its natural provenance and unenhanced state are integral to its value and character.

The sapphire derives its optical performance from the intrinsic properties of corundum and from precise lapidary geometry. Corundum has a high refractive index, typically around 1.76 to 1.77, and a modest birefringence near 0.008, which together govern how light is bent and split as it travels through the crystal. Though dispersion in sapphire is lower than in diamond, the high refractive index, combined with the clarity and polish of this stone, produces a vivid return of light and distinct contrast between bright facets and shadowed facets. The mixed brilliant cut accentuates this effect by using brilliant style facets on the crown to create concentrated flashes of light, and step style facets on the pavilion to form crisp, reflective planes. The result is a scintillation that reads as lively sparkle during movement, and a balanced brightness when viewed face up. The bi color phenomenon in this specimen is a consequence of localized variations in trace element concentrations, most commonly iron and titanium, which alter absorption across the crystal lattice and produce a natural color zoning from blue into yellow green. As the stone is rotated, the subtle pleochroic tendencies of corundum allow distinct color zones to emerge and recede, adding a dynamic visual depth that complements the facet driven sparkle.

Beyond optics, the physical resilience and surface quality of corundum amplify the perception of brilliance. With a Mohs hardness of 9, sapphire holds crisp facet junctions and maintains a high polish, both of which are evident in the excellent polish grade of this stone. Very slight inclusions that are only apparent at eye level preserve overall transparency, enabling uninterrupted light transmission and minimizing light leakage. The dimensions and depth yield a compact and wearable 0.51 carat oval that will sit confidently in a variety of settings, where the mixed brilliant design will interact with surrounding metals to emphasize contrast and brightness. The Natural Sapphire Company confirms the stone is natural and unheated, attributes that ensure the bi color character and clarity are intrinsic rather than induced. Taken together, the corundum crystal structure, the skilled mixed brilliant cutting, the unenhanced origin, and the meticulous polish produce a sparkle and color interplay that distinguishes this bi color sapphire from more commonplace stones, making it a technically refined and visually engaging gem.