What it is confused with
Blue sapphire, iolite, glass and synthetic forsterite, which is sold as a tanzanite imitation.
Violet blue to deep purple
Tanzanite birthstone
Tanzanite, the birthstone for December, is calcium aluminum silicate (Ca₂Al₃(SiO₄)₃(OH)) — blue zoisite, violet blue to deep purple, rated 6–7 on the Mohs scale. Traditionally, it is linked to perspective shifts and seeing a situation from above — attributed, not demonstrated.
- Mohs hardness
- 6–7 scratches window glass
- Crystal system
- Orthorhombic Ca₂Al₃(SiO₄)₃(OH)
- Main sources today
- Tanzania (Merelani Hills — the only source on Earth)
Is Tanzanite a birthstone?
Yes. Tanzanite is the modern birthstone for December.
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Properties
Composition
Calcium aluminum silicate (Ca₂Al₃(SiO₄)₃(OH)) — blue zoisite
Hardness (Mohs)
6–7
Crystal system
Orthorhombic
Color
Violet blue to deep purple
Mined in
Tanzania (Merelani Hills — the only source on Earth)
Worth knowing
Mined in a strip of land roughly seven kilometres long. At current rates the deposit is expected to run out within decades.
History
Found in 1967 and named by Tiffany & Co. the following year.
Buying
Buying Tanzanite: fakes, value and treatments
What decides the price
Deep violet-blue is valued most. Nearly all tanzanite is heated to turn brownish zoisite blue, a stable and accepted treatment.
Where it is used
Fine jewelry, often set in protective settings because the stone is relatively soft.
A less familiar fact
It comes from a single small mining area in the Merelani Hills of Tanzania and shows blue, violet or burgundy depending on the viewing angle.
Practical
Caring for Tanzanite
How to clean it
Warm soapy water and a soft brush. No ultrasonic, no steam — tanzanite is sensitive to sudden temperature change.
How to tell it is real
Effectively all tanzanite is heat-treated to produce the blue; unheated material is brown and rare. Coated imitations exist and need a lab to separate.
How hard is Tanzanite?
Tanzanite is soft for a faceted gem and has one direction of perfect cleavage, so it scratches more easily than sapphire and can crack from a knock or sudden heat. It is safer in earrings and pendants than in an everyday ring. Only Jade shares its place on our scale. Among the stones in this reference, the next softer is Moonstone (6–6.5) and the next harder Bloodstone (6.5–7).
Tanzanite, at 6–7, is harder than 17 of the other 42 stones here and softer than 24.
Traditional associations
Tanzanite is traditionally linked to perspective shifts and seeing a situation from above. Chakra in crystal practice: Third Eye, Crown. Element: Air.
Questions about Tanzanite
What is Tanzanite made of?
Calcium aluminum silicate (Ca₂Al₃(SiO₄)₃(OH)) — blue zoisite, crystallizing in the orthorhombic system.
Which month is Tanzanite the birthstone for?
December.
Where does Tanzanite come from?
Tanzania (Merelani Hills — the only source on Earth).
Can Tanzanite be worn every day?
With care. At 6–7 on the Mohs scale it can be worn often, but watch out for knocks and sudden heat, because it cleaves.
Cite this page
AstroHot. “Tanzanite Birthstone: The December Stone and Its Meaning.” Accessed October 28, 2026. https://astrohot.com/crystals/gemstones/tanzanite/
For Wikipedia
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