Most tanzanite is brown when it comes out of the ground. Heat treatment turns it blue. The rough stone is heated in a furnace to between 500°C and 600°C for a few hours, and the brown fades to leave the deep blue and violet colours tanzanite is famous for.
Heating is normal and accepted for tanzanite. Almost every stone on the market has been heated, and it is still a real, valuable gem. This guide explains the heat treatment process of tanzanite, why it is heated and how to tell if a stone has been heated. You can see real stones in our tanzanite collection.
What is tanzanite?
Found in one place only. Tanzanite is a rare gemstone found in just one place on Earth: Tanzania. It is famous for its deep blue and violet colours.
Colour that shifts with the light. Many people love tanzanite because it can look blue or violet in different lights.
Why is tanzanite brown at first?
Trapped minerals. Tanzanite forms deep inside the Earth under high heat and pressure over millions of years. While it forms, tiny amounts of other minerals get trapped inside. These affect the colour and make the stone look brown or dull.
Brown or yellow in the rough. Before heating, about 90% of tanzanite is brown. Some rough stones show yellow tones too.
Why is tanzanite heated?
To bring out the blue. Heating removes the brown and yellow tones and leaves the stone bright blue or violet. Without it, most tanzanite would stay brown and would not be as beautiful or valuable.
It makes tanzanite more affordable. Because heating turns brown rough into blue gems, many more stones can be used in jewellery. That keeps tanzanite within reach for more people.
The heat treatment process of tanzanite, step by step
- Into the furnace: the stone is placed in a special furnace or oven.
- Careful heating: it is heated to a high temperature, between 500°C and 600°C. This is done carefully so the stone does not break or get damaged.
- The brown fades: the heat acts on the iron and vanadium inside the stone, and the brown and yellow tints disappear.
- Blue and violet appear: the stone shows its famous blue, violet or purplish shades.
- Cooling and checking: the heated stone is cooled down and checked for quality.
A few hours. The whole process takes a few hours and does not harm the gem. It improves the colour, which makes the stone more beautiful and valuable.
Is heat-treated tanzanite natural or fake?
It is real tanzanite. Many people think heating makes a gem fake, but this is not true. Heating is a natural way to bring out a stone's best colour. It does not involve any chemicals, dyes or harmful substances. The stone remains 100% real and natural, just with a better colour.
Standard in the trade. About 99% of tanzanite on the market has been heated, and this is accepted across the gemstone industry.
Does heating affect the quality of tanzanite?
No. Heating does not change the structure or quality of the gem, only its colour. Tanzanite stays strong after heating.
One care point. Do not expose tanzanite to sudden temperature changes, as this can cause cracks.
Can tanzanite change colour again after heating?
No, the colour is permanent. Once tanzanite has been heated, its blue or violet colour stays the same and will not fade over time, unless the stone is exposed to strong heat again. That makes it a lasting choice for jewellery.
Blue and violet in one stone. After heating, some tanzanite shows both blue and violet depending on the lighting. This is called trichroism.
Are there natural blue tanzanites?
Yes, but they are very rare. Only a small number of tanzanites come out of the ground with a natural deep blue colour. Natural blue tanzanite is so rare that only one in a million stones is found with its perfect colour. These stones are very expensive and hard to find.
How to tell if tanzanite has been heated
Assume a deep blue stone has been heated. Because almost all tanzanite is heated, it is safe to assume a deep blue stone has been through the process. Signs to look for:
- Bright, even colour: heated tanzanite has a deep blue or violet colour without brown or green tints.
- Brown shades: unheated tanzanite often has brown or yellowish areas inside the stone.
- A certificate: if you buy tanzanite with a gemstone certificate, it will tell you whether the stone has been heated.
- An expert test: for a definite answer, a gem expert can test the stone.
Is heat-treated tanzanite still valuable?
Yes. Heated tanzanite is real and highly valuable. It is not seen as fake or altered in a bad way, but as a normal step that helps the stone reach its full beauty. Experts agree heat treatment is normal for tanzanite and does not reduce its value.
Where unheated stones fit. Naturally blue, unheated tanzanite is extremely rare and can cost more. Heated or not, tanzanite is a rare and precious gem that people love to wear.