7.41 Ct. Blue Tanzanite from Tanzania

This offering from The Natural Gemstone Company is a single, transparent blue tanzanite weighing 7.41 carats, presented in a classic emerald cut. The stone measures 13.56 by 10.01 by 6.21 millimeters, yielding a length to width ratio of approximately 1.36 and a depth of about 52.7 percent when calculated against the average of length and width. The cut is a stepped emerald style with truncated corners, a broad rectangular table, and parallel crown and pavilion step facets that emphasize color planes rather than high frequency scintillation. The gem is graded eye clean at normal viewing distance, with vivid color intensity and an excellent polish. The material is natural tanzanite from Tanzania and has been heat treated, a stable and industry standard enhancement that selectively reduces brown zoning to strengthen the blue violet spectrum.

From a lapidary perspective the emerald cut is an intentional choice to showcase this tanzanite because step faceting and a large table present broad, velvety flashes of saturated blue and violet rather than the pinpoint sparkle associated with brilliant style cutting. The cutter has aligned the pavilion and crown facet planes to the crystallographic axes to best exploit tanzanite trichroism, producing a predominately blue face up color while allowing controlled violet flashes at certain viewing angles. The excellent polish produces crisp facet junctions and a mirror like finish on each step facet, which maximizes surface reflectance and creates a hall of mirrors effect within the stone. The relatively shallow to moderate depth preserves table size and face up appearance, concentrating the vivid hue and preventing excessive light leakage, which would otherwise dilute the apparent saturation in larger step cut stones.

Optically, tanzanite exhibits strong trichroism and noticeable birefringence, properties that distinguish it from many other blue gem materials. Typical refractive indices for tanzanite fall in the range of approximately 1.69 to 1.71 with birefringence on the order of 0.014 to 0.018, and dispersion that is modest compared to highly dispersive gems. In comparison, corundum in the blue sapphire variety has higher refractive indices around 1.76 to 1.78 and therefore returns more internal brilliance under broad spectrum light, with similar dispersion but much higher hardness and durability. Blue spinel, with refractive indices near 1.72, displays lively brilliance and strong surface luster, but lacks the trichroic color dynamics of tanzanite. Aquamarine and other beryls have lower refractive indices near 1.58 and consequently show less brilliance and a paler, more uniform tone. What sets this Tanzanian tanzanite apart is the interplay of deep blue and violet within the large, flat facets of the emerald cut, producing broad color flashes and a luxurious, velvety depth that is different from the sparkle oriented appearance of sapphire and spinel.

For practical use and longevity, the gemological and handling considerations are straightforward. Tanzanite has moderate hardness and will benefit from settings that protect the girdle and edges, such as bezel settings, protective prongs, or designs that incorporate a channel or halo to absorb knocks and wear. The eye clean clarity and excellent polish mean the stone can be set with minimal risk of visible windows or localized color loss, and the heat treatment disclosed is stable and standard in the trade for improving face up color. Routine care should avoid sudden extreme temperature changes and aggressive abrasion, and professional ultrasonics and steam cleaning are generally not necessary for daily maintenance. At The Natural Gemstone Company we can provide additional documentation and imagery on request, advise on setting options to balance protection with light entry for maximum color presentation, and supply a certificate that records origin, enhancement status, and our assessment of clarity and cut, ensuring that this 7.41 carat emerald cut blue tanzanite is presented with full technical transparency and artisanal consideration.