Tanzanite Buying Guide: Natural vs Lab-Grown, Prices per Carat & Quality

What is tanzanite?

Tanzanite is the blue-violet variety of zoisite, found commercially only near Merelani, Tanzania. Hardness: 6–7 on the Mohs scale.

Colour and quality factors

Deep, saturated violet-blue is most valued; pleochroism shows blue and purple from different angles. Retail 'AAA' grades are seller grades, not lab standards.

Origins and natural (mined) stones

Single commercial source in Tanzania, which supports rarity narratives but supply has been steady.

Carat weight and size

Large clean stones (5–20 ct) are available; colour deepens with size, so larger stones often look richer.

Prices per carat

Light colour: roughly $100–$300/ct. Fine deep colour 3–10 ct: roughly $400–$1,200/ct. Exceptional: higher. These are indicative retail ranges per carat gathered from published trade and auction reporting; real prices vary widely with colour, size, origin and treatment, and are not a Riakoob quote.

Natural vs lab-grown (synthetic)

There is no widely marketed lab-grown tanzanite; synthetic forsterite, glass and coated stones are sold as simulants. Under US FTC guidelines a lab-made stone must be clearly described as laboratory-grown, laboratory-created or synthetic, never simply by the gem name.

Treatments you must know about

Nearly all tanzanite is heated to remove brown; coatings also exist and should be disclosed. Treatment disclosure is required; ask for it in writing and on the lab report.

Certification

For significant tanzanite purchases, ask for a report from an independent lab such as GIA, AGL, SSEF or Gübelin stating natural or synthetic origin, any treatments and, where relevant, geographic origin.

Care and durability

Softer and can cleave; avoid ultrasonic, sudden temperature changes and hard knocks. Better in earrings and pendants or protective ring settings.

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