Tanzanite
Tanzania's signature gemstone from the Merelani Hills - single-source rarity, colour grades, and heat treatment.
By Fabian Moor
Last updated
tanzania tanzanite zoisite single-source merelani
Introduction
Tanzanite is Tanzania's signature gemstone and one of the most remarkable
gem discoveries of the 20th century. Found only in a small area near Mount
Kilimanjaro, its unique violet-blue colour and single-source rarity have
made it highly desirable.
Discovery & Source
Characteristics
Distinctive properties that define tanzanite:
- Species: Zoisite (calcium aluminium silicate)
- Colour: Violet-blue to blue-violet
- Pleochroism: Strong; blue, violet, burgundy axes
- Heat treatment: Nearly universal; improves colour [2]
- Hardness: 6-7 (requires careful setting)
- Cleavage: Perfect in one direction (care needed)
Colour Grades
Understanding tanzanite colour quality:
Exceptional
- Vivid violet-blue colour
- Strong saturation throughout
- Medium to medium-dark tone
- Commands highest prices
Fine
- Strong blue with violet modifier
- Attractive, well-saturated colour
- Good market demand
Good/Commercial
- Lighter blue-violet
- Visible colour but less saturated
- Accessible price points
Viewing Considerations
- Direction dependence: Colour varies significantly with viewing angle
- Best face-up: Cutters orient for optimal blue/violet balance
- Lighting: Appears more violet under incandescent light
Heat Treatment
Standard enhancement for tanzanite:
- Purpose: Removes brown/yellow component, enhances blue-violet
- Prevalence: Nearly all commercial tanzanite is heated
- Detection: Very difficult; generally assumed
- Unheated: Rare; some collectors seek natural colour
- Disclosure: Treatment generally assumed and accepted
Single Source Concern
Market Position
References
- ↑ 1. Schumann, W. (2009). Gemstones of the World (4th ed.). Sterling Publishing. ISBN: 978-1-4027-6829-3.
- ↑ 2. Read, P. (2014). Gemmology (3rd ed.). Butterworth-Heinemann. DOI: 10.4324/9780080507224.