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Tanzanite
ORTHORHOMBIC

Tanzanite

Ca2Al3(SiO4)3(OH)

Hardness
6–6.5
Refractive Index
1.69–1.70
Spec. Gravity
3.2–3.4
System
Orthorhombic
Tanzanite is the blue to violet gem variety of the mineral Zoisite. Since its relatively recent discovery in 1967, it has become a mainstream and popular gemstone, and is used extensively in jewelry. To date, Tanzanite is found only in the Arusha region of the African country of Tanzania, and it was named after its country of origin.

About

The name Tanzanite was coined in 1969 by Henry Platt, the vice-president of prominent jewelery company Tiffany and Co. Tiffany expended much effort marketing this new gemstone with its new name, and Platt's efforts paid off with this gemstone becoming extremely popular in a short period of time. The name Tanzanite caught on and is now a standard name in the gem trade.

The main appeal of Tanzanite is its lovely color. Its color ranges from pure blue to purplish-blue. It is highly pleochroic, and will display different color saturation when viewed at different angles. Planning is required when faceting a Tanzanite gemstone in order to cut it at an angle that delivers the stronger blue color rather than the duller gray tone. Care must also be exercised during faceting to prevent chipping, since this gemstone has perfect cleavage in one direction. For this same reason, Tanzanite jewelry should not be banged against hard surfaces and should be worn carefully.

Tanzanite is a relatively soft for gemstone. This places somewhat of a limitation on its uses and care must be taken to protect it from being scratched. Tanzanite also has a low resistance to ultrasound and should not be cleaned with ultrasound cleaners as this may cause the gemstone crack. Although Tanzanite has a lovely color and appeal, it does have several limitations in its durability.

Uses

Tanzanite is a very popular jewelry gemstone. It is used in bracelets, necklaces, and earrings. It is less often used in rings due to its relatively low hardness which makes its prone to scratches. Lesser quality stones are occasionally cut into cabochons.

Varieties

✓ common  · ✗ uncommon

  • Yellow Tanzanite— Rare yellow transparent Zoisite from Arusha, Tanzania. It is found in the same deposits associated with Tanzanite, and is essentially the same as Tanzanite except for its color which is different.

False Names

Treatments & Enhancements

Tanzanite gemstones are always heat treated. Natural Tanzanites have a more dull gray, greenish, or brownish color, and heating to above 800 degrees Fahrenheit (about 430 Celsius) will produce the deep blue to violet color.

Sources

The world's only source of Tanzanite is the Merelani Hills, Arusha, Tanzania.

Similar Gemstones

The violet hue of Tanzanite gives it a unique color. It closely resembles Iolite, but it can be distinguished by its lower refractive index and specific gravity. Iolite is also usually a darker tone. Tanzanite lacks the deep purple hue of Amethyst, and is usually more purple than blue Sapphire. It may resemble some tints of purple Sapphire, but can be distinguished by its much lower hardness.

Further Reading

Faceted

In the Rough

See all 10 in the rough photos →

Jewelry