Tanzanite Stone Guide

Tanzanite is gem-quality zoisite coloured by trace vanadium. It was discovered by Maasai herders in 1967 and introduced to the world by Tiffany & Co. in 1968. It comes from a single deposit a few kilometres long, so supply is finite. Tanzanite is strongly pleochroic, showing blue and violet from different crystal directions.

Rich blue to violet. In daylight tanzanite leans bluer, under incandescent light it reads more violet. The most prized stones are a vivid, saturated blue-violet that holds across light sources. Lighter lavender-blue tanzanites are gentler and more affordable.

Tanzanite is 6 to 7 on the Mohs scale with fair toughness and some directional weakness, so it can chip from a sharp knock. It is also sensitive to sudden temperature changes. Not the right stone for a ring worn every day on a hand that does heavy work. Earrings, pendants and protected ring settings hold up much better.

Colour saturation is the main driver. A vivid, deeply saturated blue-violet is worth far more than a pale stone of the same size. Clarity should be eye-clean. Cut matters because tanzanite is cut to balance the blue and violet directions of the crystal. Larger stones over 5 carats show colour more strongly.

Almost all tanzanite is heat treated to remove brown tones and bring out the blue-violet colour. The treatment is stable and accepted. There is no commercial alternative source for natural tanzanite outside the Merelani Hills in northern Tanzania, which is why supply is genuinely finite.

Earrings and pendants are the safest choice. Statement cocktail rings and occasion rings work well in protective settings like bezels. Tanzanite engagement rings are possible but should be reserved for buyers who understand the trade-offs and treat the ring gently.

Clean only with warm soapy water and a soft cloth. Never use ultrasonic or steam cleaners. Avoid sudden temperature changes. Store separately from harder gemstones. Remove tanzanite rings before housework, exercise and rough activity.

Vivid tanzanite over 5 carats with strong blue-violet colour reaches premium prices. Smaller commercial stones are widely available at sensible prices. Because the source is finite, prices for the best stones have trended up over the long run.