Tanzanite
(tan-zuh-nahyt)
HISTORY and LORE
- First identified in the early 1960’s. Major deposits were discovered a few years later. Since then tanzanite has become a favorite colored gem around the world.
- Named for Tanzania, the East African nation where it was originally found.
- December birthstone and gem for the 24th wedding anniversary.
VALUE FACTORS
- Color: Light to dark purple, violet, or blue. Most expensive is deep pure blue. May show noticeable color shift – more bluish in daylight or fluorescent, and more purplish in incandescent light.
- Clarity: Often almost inclusion-free.
- Cut: Faceted in many shapes and styles.
- Carat Weight: Normally available in all jewelry sizes (up to 15 or 20 carats).
TREATMENT
Virtually all tanzanite is heat treated to develop its color. A popular story says the possibility of treatment was recognized when a wildfire changed crystals lying on the ground from pale brown to rich blue. The treatment’s effects are normally permanent, and it creates no added special care requirements for gem owners.
GEMOLOGY
- A variety of the mineral species zoisite. Zoisite more commonly occurs in translucent to opaque green or pink, and rarely in transparent green.
- Tanzanite has a complex chemical formula that includes calcium, aluminum, silicon, oxygen, and hydrogen. Color caused by trace amounts of vanadium.
CARE
Tanzanite needs gentle wear and care. Protective setting is recommended.
- Hardness: Moderate scratch resistance. Rates 6 to 7 on the Mohs Hardness Scale
- Toughness: Fair to low resistance to chipping and breaking because of cleavage (a tendency to split in certain directions due to crystal structure patterns).
- Stability: Sensitive to thermal shock. Rapid temperature change can cause breaks.
- Cleaning: Liquid cleaner, or detergent and water. NEVER USE AN ULTRASONIC.