Stone library / Other Silicate Gemstones / Zoisite Group
Tanzanite
Everything you need to know about tanzanite: what it is, where it comes from, treatments, jewelry care, cultural meaning, and what affects value.
Traditional birthstone: December (alternative).
Note: Found only in Tanzania. Limited supply as the single source is finite. Named by Tiffany & Co. in 1968.
What is tanzanite?
Tanzanite has chemical formula Ca₂Al₃Si₃O₁₂(OH) (zoisite with vanadium). Mohs hardness: 6.5–7. Density: approximately 3.35 g/cm³. Refractive index: 1.69–1.70.
What gives it its color?
Vanadium (V) produces blue-violet color. Most tanzanite is heat-treated to convert brownish zoisite to blue-violet.
Where does it come from?
Major sources include Tanzania (exclusively — a single mining area near Mount Kilimanjaro).
Treatments and how to spot them
Nearly all commercial tanzanite is heat-treated (~400-500°C) to produce the blue-violet color. Untreated brown zoisite is rare in the market.
Important: Visual clues such as inclusions, color patterns, or surface features can provide preliminary observations, but they cannot replace refractive index, specific gravity, microscopic examination, and laboratory testing for a definitive identification. Treat visual clues as starting points, not final answers.
Jewelry and care tips
With hardness 6.5–7, tanzanite can be used in various jewelry types. Clean with warm soapy water and a soft cloth. Avoid ultrasonic cleaners unless the stone is known to be fracture-free. Store separately from harder gemstones.
Note: Prolonged strong light or high heat may cause some color-sensitive or treated stones to fade. Brief daily wear does not usually cause immediate fading, but avoid leaving jewelry in direct sun for extended periods.
Cultural beliefs and symbolism
Tanzanite carries cultural meaning across many traditions — these are folkloric and cultural traditions, not scientifically verified properties. Its associations vary by culture, and its use in astrology, chakra, or feng shui contexts should be understood as cultural expression rather than factual claims.
What affects its value?
Price is determined by color saturation, clarity, cut quality, and size. Terms like commercial color names are market descriptions — they cannot by themselves prove origin or value. Before buying: ask the seller to confirm the material identity, treatment status, dimensions, and return policy in writing.
Use this guide as a starting point
For a costly or disputed stone, ask for species, treatment, and origin information in writing. An independent laboratory report is stronger evidence than a marketing phrase.
Return to Other Silicate GemstonesSources: GIA reference and the GemVerity editorial method. This is an educational guide, not a gemological identification report. Cultural beliefs described above are folkloric traditions, not scientific guarantees.