Judging quality
Look for deep blue with violet flash rather than pale washed tones. Trichroism means color varies with orientation; heat treatment is universal and expected.
Zoisite
Tanzanite
Blue-violet zoisite found in a single four-square-mile stretch of northern Tanzania. Almost all material is heat-treated to convert brownish rough into blue.
Care
Relatively soft with one cleavage direction and sensitive to sudden temperature change. Never ultrasonic.
History & lore
Discovered in 1967 and named by Tiffany & Co., which judged 'blue zoisite' unmarketable.
Cultural history, recorded as tradition rather than as medical or scientific claim.
Common questions about Tanzanite
- What is Tanzanite?
- Blue-violet zoisite found in a single four-square-mile stretch of northern Tanzania. Almost all material is heat-treated to convert brownish rough into blue.
- How hard is Tanzanite and what is it made of?
- Tanzanite is a Zoisite-family mineral with the composition Ca2Al3(SiO4)3(OH). It crystallizes in the orthorhombic system and rates 6-7 on the Mohs hardness scale. It occurs in violet, blue.
- Where does Tanzanite come from?
- Notable localities for Tanzanite include Tanzania (Merelani Hills).
- How do you tell good Tanzanite from filler?
- Look for deep blue with violet flash rather than pale washed tones. Trichroism means color varies with orientation; heat treatment is universal and expected.
- How do you care for Tanzanite?
- Relatively soft with one cleavage direction and sensitive to sudden temperature change. Never ultrasonic.
See it in person
Photographs only go so far
Both rooms are open six days a week, and there is always someone happy to pull pieces out of the case so you can compare them under the light.