Tanzanite: the complete guide, from the source

Tanzanite is mined commercially only in the Merelani Hills, in the Manyara region of northern Tanzania, between Arusha and Moshi and in sight of Kilimanjaro. Because there is a single source, every genuine tanzanite comes from Tanzania, and buying close to the mines means buying close to the people who know the stone best.

Our owner Mrema has spent over 20 years sourcing stones directly from the field and cutting them in our Moshi workshop. Each stone in our tanzanite collection is hand-selected before it reaches our showroom.

Tanzanite shows different colours when viewed from different directions, an effect called pleochroism. In a cut stone you see a blend of blue and violet as it moves. Cool, daylight-like light makes it look bluer; warm indoor light brings out the violet.

• Blue to violetish blue is the most sought-after colour, especially when deep and saturated.
• Violet to bluish purple is more common and loved for its rich, royal look.
• Green, pink and colourless zoisite come from the same mineral. They are rarer and unusual. See our green, pink and white tanzanite.

Four things decide what a tanzanite is worth. Colour matters most.

1. Colour: strongly saturated blue or violetish blue commands the highest prices; lighter, pastel stones are more affordable.
2. Size: tanzanite usually needs some size to show deep colour, so larger stones (often 5 carats and up) can show the richest blue, and the price per carat rises with size.
3. Cut: a well-cut stone returns light evenly across its whole face. The cutter also chooses which colour faces up.
4. Clarity: most tanzanite is eye-clean; visible inclusions or fractures lower the value.

There is no single official grading scale, so labels like “AAA” are set by each seller. That is why we show the carat weight and the price per carat on every stone. See our tanzanite price guide for real prices.

Most tanzanite is gently heat-treated, a standard practice that removes brownish or yellow-green tones and brings out the blue and violet. Our tanzanite is heat-treated, and we say so on every stone.

Every stone we sell comes with a GIA certificate and our own Gemstone Cutter (T) Investment certificate, so you know exactly what you are buying.

• Tanzanite is 6 to 7 on the Mohs hardness scale, softer than sapphire, so protect it from hard knocks.
• Clean it with warm water, mild soap and a soft brush.
• Never use ultrasonic or steam cleaners, and avoid sudden changes of temperature.
• Store it apart from harder gems and diamonds, which can scratch it.

Tanzanite is a December birthstone and the traditional gift for a 24th wedding anniversary. A tanzanite pendant or ring makes a meaningful gift, or we can make a piece to order.

Our showroom is in Kibo Tower Building, Ground Floor, Room 4B, Moshi. Follow the “Tanzanite Dealer” sign in the corridor. We are open Mon–Sat 8:30 am – 6 pm, Sun 9 am – 5:30 pm. See the stones in daylight, ask questions, and take your time. If you can't visit, order online: we call to confirm before you pay, and we ship worldwide.

Visiting Tanzania? Read our guide to buying tanzanite safely in Tanzania and how to find us.