Zoisite · December birthstone
Tanzanite
Found in one place on earth, blue by day and violet by lamplight.
- Hardness
- Mohs 6.5
- Toughness
- Fair to poor
- Daily wear
- Earrings and pendants
- Price tier
- USD 300 to 1,200 per carat, fine quality
- Colours
- Blue, Violet, Blue-violet
- Origins
- Tanzania (Merelani Hills only)
Tanzanite is blue-violet zoisite from a single deposit near Mount Kilimanjaro, discovered in 1967 and named by Tiffany. It shows different colours from different directions (pleochroism), shifting from blue to violet. Virtually all tanzanite is heated. It is soft and brittle, which makes it a stone for earrings, pendants and occasional rings.
How to buy tanzanite
Prefer saturated blue with a violet flash over pale lavender. Larger stones show better colour. Buy for the colour, not for investment: supply is finite but not yet scarce.
Treatments
Heating is universal and accepted; it turns brown zoisite blue.
Care
Warm soapy water only; never ultrasonic or sudden temperature changes.
Lore
One of the few gemstones with a known discovery date. Added to the birthstone list for December in 2002.
