Tanzanite Buying Guide: The World’s Rarest Single-Source Gem
Tanzanite is one of the most extraordinary gemstone success stories of the 20th century — and one of the most compelling sales narratives in the jewelry trade. Discovered in 1967 in a single location near Arusha, Tanzania, it is found nowhere else on earth. Its geological formation window is so specific that it will not form again — what exists in the Merelani Hills is all that will ever exist. For a jewelry professional, tanzanite combines a magnetic sales story with genuine gemological fascination.
Mineralogy and Optical Properties
Tanzanite is the blue to violet variety of zoisite (calcium aluminum silicate), colored by vanadium. Its Mohs hardness is 6 to 7, which is softer than sapphire or ruby and requires some care in ring settings — bezels and protective settings are preferable to high prong settings for frequent-wear rings. Tanzanite is strongly trichroic: it displays three distinct colors from three crystallographic axes — blue, violet, and burgundy/brown. Careful cutting orients the stone to show the desirable blue-violet face-up.
Refractive index: 1.685 to 1.707. Specific gravity: 3.10 to 3.38. Tanzanite has perfect cleavage in one direction — a potential durability weakness if the stone receives a sharp impact at the right angle. For earrings, pendants, and protective ring settings, durability concerns are minimal.
The Heat Treatment Reality
Virtually all tanzanite on the market has been heat treated. Natural tanzanite rough is typically brownish-yellow to greenish, with the desirable blue-violet color being enhanced or revealed by heating at approximately 600 degrees Celsius. The treatment is stable, permanent, and universally practiced — it does not require disclosure in the same way that, say, fracture filling does, because it is universally understood to be industry standard.
A small percentage of tanzanite naturally occurs blue-violet without heating. Such stones are often called “blue tanzanite” in the trade but command no significant premium in the commercial market because the treatment result is indistinguishable from natural blue color by standard gemological testing.
The AAA Grading System
The tanzanite trade uses a proprietary color grading system, with AAA being the highest commercial grade. While not an industry-wide standard like diamond grading, the AAA designation has become universally understood in the trade. Understanding what constitutes top-grade tanzanite is essential for accurate pricing and presentation.
AAA (Top Grade)
Deep, vivid blue-violet color with excellent saturation and medium-dark tone. Face-up color shows both blue and violet components without one overwhelming the other. Strong color change from blue in daylight to violet in incandescent light. Excellent transparency and few visible inclusions. Less than 1 percent of tanzanite production reaches AAA quality.
AA (Fine Grade)
Very good blue-violet color, slightly lighter or slightly less saturated than AAA. Minor visible inclusions acceptable. Represents approximately 5 to 10 percent of production.
A and Commercial Grades
Lighter, less saturated blue to violet. May lean more toward violet than blue or show a grayish modifier. Visible inclusions more common. The majority of commercial tanzanite falls in this range.
The Scarcity Narrative — True and Powerful
No other gemstone offers a single-source scarcity story like tanzanite. Mines in the Merelani Hills of Tanzania are the only known commercial deposit in the world. The Tanzanian government has divided the mining area into Blocks A through D, with small artisanal miners working alongside larger operations. Mining depths increase each year as shallow reserves are exhausted.
Geologists consistently note that tanzanite is a geological accident — the precise combination of vanadium-rich hydrothermal fluids, regional metamorphism, and oxidation conditions that created the deposit are not found elsewhere. The supply is finite and diminishing. This is not marketing hyperbole — it is geological fact and a legitimate value driver.
Color Change and Pleochroism
Tanzanite’s dramatic color behavior under different light sources is one of its most compelling display properties. Under cool daylight or fluorescent light, fine tanzanite appears predominantly blue with a violet secondary hue. Under incandescent light (tungsten or candlelight), the same stone appears more violet or purplish. This chameleon quality is endlessly fascinating to customers and should be demonstrated whenever possible using different light sources in your display environment.
Sizing and Pricing Considerations
Tanzanite is available in a wide size range and prices scale with quality and size. AAA quality becomes increasingly rare and expensive above 5ct. For commercial jewelry, the 1 to 3ct range in AA quality represents the sweet spot of beauty and price. Deep saturation is harder to achieve in smaller stones, which tend to look paler.
Care and Handling
Tanzanite should never be cleaned in an ultrasonic cleaner or steam cleaner — both can damage or crack the stone. Warm water and mild soap with a soft brush is the correct cleaning method. Avoid exposure to sudden temperature changes. Protect tanzanite rings from knocks and impacts given the perfect cleavage.
