Tanzanite blue purple

Tanzanite is a rare blue-violet variety of zoisite discovered in Tanzania, prized for its intense color and characteristic pleochroism.

About this subject

Tanzanite is a precious gemstone belonging to the sorosilicate group, specifically a variety of zoisite. It was discovered in 1967 in the Merelani Hills, near Mount Kilimanjaro in northern Tanzania, remaining the only known source in the world. Its deep blue-violet color, often compared to sapphire, results from vanadium traces in its crystal structure. The gem exhibits strong pleochroism, showing different shades of blue, violet, and burgundy when viewed from different angles. Due to its rarity (supply is estimated to last only a few more decades) and popularity boosted by Tiffany & Co., which promoted it in the 1970s, tanzanite is one of the most sought-after stones in the jewelry market. With a hardness of 6.5 to 7 on the Mohs scale, it is suitable for jewelry but requires care to avoid scratches. Mining is largely artisanal, controlled by small-scale miners, with sales regulated by the Tanzanian government. Interestingly, in 2002 the American Gem Trade Association added tanzanite as an alternative birthstone for December, alongside turquoise and blue zircon.

Frequently Asked Questions

How is tanzanite formed?

Tanzanite forms under specific geological conditions when heat and pressure transform zoisite with vanadium traces. This occurs in medium to high-grade metamorphic rocks in the Merelani Hills.

What is the difference between tanzanite and sapphire?

Tanzanite has a softer blue-violet color and shows pleochroism, while sapphire is typically more intense blue and belongs to the corundum group. Tanzanite is softer (6.5-7 Mohs) compared to sapphire (9 Mohs).

Is tanzanite heat-treated?

Most commercial tanzanite is heat-treated to enhance blue color. The treatment is stable and accepted in the market, but untreated stones are rare and more valuable.