TANZANITE
Tanzanite
Zoisite
The blue-to-violet variety of zoisite, commercially sourced from the Merelani area in northern Tanzania.
GEM PROFILE
Basic properties
- Mineral or material
- Zoisite
- Main chemical composition
- Ca₂Al₃(SiO₄)₃(OH)
- Crystal & structure
- Orthorhombic
Pleochroism produces different colors along different crystal directions.
- Typical colors
- Blue, violet-blue and bluish violet
- Mohs hardness
- 6–7
A measure of scratch resistance, distinct from resistance to impact or breakage.
About hardness and durability - Representative sources
Examples of known sources. Determining the origin of an individual stone requires examination and comparison with reference material.
- Common cutting styles
- Ovals, cushions and trillions, oriented with pleochroism in mind.
Explore cutting styles
LOOK A LITTLE CLOSER
What to observe
Its visible color changes with angle. Consider its susceptibility to breakage as well as hardness when wearing it in jewelry.
TREATMENT & CARE
Treatments & care
Treatments & identification
Many stones are heated to develop their blue-to-violet appearance.
Everyday care
Protect against impacts and rapid temperature changes. Avoid ultrasonic or steam cleaning; use lukewarm water and mild detergent.
Cleaning depends on treatment, inclusions and mounting. If a stone's condition is unknown, ask your jeweler or a gem specialist before cleaning.
READING & REFERENCES
References
Public sources for learning about this gemstone's general properties.
- GIA · Gemological reference
- GIA · Care & Cleaning
- Handbook of Mineralogy · Mineral data (PDF)
- GIA · Gem sources and fundamentals
This dictionary provides general educational information. Values are representative and do not identify or grade an individual stone. Locality examples include historical deposits.
Sources checked: October 19, 2026