Tanzanite
Found in only one place on earth — a violet-blue stone rarer than diamond.
Tanzanite is the blue-violet variety of the mineral zoisite, discovered in 1967 near Mount Kilimanjaro in Tanzania. It is found in a single deposit roughly 4 km wide, making it approximately 1,000 times rarer than diamond by geological occurrence. Tiffany & Co. named the stone and introduced it to the market in 1968. Tanzanite is strongly trichroic, showing different colors (blue, violet, and burgundy) depending on the crystal axis and viewing angle. Nearly all tanzanite on the market has been heat-treated to shift its color from brownish to the prized blue-violet.
Physical Properties
| Hardness (Mohs) | 6–6.5 |
| Refractive Index | 1.691–1.700 |
| Specific Gravity | 3.35 |
| Crystal System | Orthorhombic |
| Chemical Formula | Ca₂Al₃(SiO₄)(Si₂O₇)O(OH) |
Color Varieties
Major Sources
Tanzania (sole source)
Pricing Factors
Color Saturation
Deep, vivid violet-blue stones command the highest prices. Lighter 'lavender' tanzanites are more affordable. The most prized shade shows a balance of blue and violet.
Size
Prices escalate significantly above 5 carats. Fine-quality stones above 10 carats are genuinely rare and carry exponential premiums.
Clarity
Tanzanite is a Type I gem — eye-clean clarity is expected. Visible inclusions significantly lower value.
Market Supply
As a single-source gem, tanzanite supply is finite. Mining disruptions and export regulations from Tanzania directly impact global pricing.
Care Instructions
Do
- Clean with lukewarm soapy water and a soft cloth
- Store in a padded box away from harder stones
- Best suited for earrings, pendants, and occasional-wear rings
Don't
- Never use ultrasonic or steam cleaners
- Don't wear in rings for daily use — tanzanite is too soft
- Avoid sudden temperature changes (thermal shock can cause fractures)
Cleaning Method
Lukewarm soapy water only. Tanzanite is sensitive to heat, pressure, and sudden temperature changes. Handle with care.
Insider Buying Tips
Tanzanite is best for earrings and pendants — it's too soft for an everyday engagement ring.
Heat treatment is universal and accepted — there's no market premium for 'natural color' tanzanite.
Buy the deepest saturation you can afford — pale tanzanite looks generic, but saturated stones are genuinely stunning.
Consider tanzanite as an investment play — the single-source supply is finite and mine production is declining.
Verify that the stone has not been coated (a treatment that wears off) — ask for a gemological report.
Did You Know?
Tanzanite was formed 585 million years ago during massive tectonic plate activity.
Geologists estimate the mines could be depleted within 20–30 years at current extraction rates.
Tiffany & Co. named the stone 'tanzanite' because they felt its scientific name (blue zoisite) was unmarketable.
Related Resources
Related Gemstones
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Spinel
The great imposter — historically mistaken for ruby and sapphire, now prized in its own right.
Tourmaline
The rainbow gem — no other mineral occurs in as many colors.