TANZANITE
Tanzanite is the blue to violet gem variety of zoisite and is famous for its vivid pleochroism, which can show different colors when viewed from different directions. It is associated with a small mining area near Mount Kilimanjaro in northern Tanzania, making documented origin especially important to its story. Most tanzanite used in jewelry is heat-treated to bring out blue-violet color, a widely accepted practice that should be disclosed accurately.
Contents
- What is tanzanite?
- Properties and color
- Pleochroism and treatment
- Origin and mining
- Identification and buying advice
- Care
- Frequently asked questions
- Sources
What is tanzanite?
Tanzanite is a gem variety of the mineral zoisite. It was brought to wider gem-market attention in the twentieth century and is now one of the best-known colored gemstones. Its blue-violet appearance, relative rarity, and restricted known commercial source distinguish it from many other gems.
Although the trade name is widely recognized, the mineral species is zoisite. Gem-quality material can range from pale blue to deep violet-blue, and the final appearance depends on color, cut, clarity, and treatment.
Properties and color
- Mineral: Zoisite.
- Crystal system: Orthorhombic.
- Hardness: About 6–7 on the Mohs scale.
- Luster: Vitreous.
- Colors: Blue, violet, and sometimes brownish or greenish tones in untreated material.
- Cleavage: Present, so sharp impacts can cause damage.
- Optical property: Strong pleochroism, with color varying by viewing direction.
Deep blue-violet stones are often sought after, but paler tanzanite can also be attractive. Cutters orient the rough to balance color, pleochroism, weight retention, and brilliance.
Pleochroism and treatment
Pleochroism is the appearance of different colors when a doubly refracting crystal is viewed along different crystallographic directions. Tanzanite may show blue, violet, and brownish components. Cutting orientation affects which colors are most visible in the finished gem.
Heat treatment is commonly used to reduce brownish tones and enhance blue-violet color. This treatment is widely accepted in the trade, but disclosure is important. A gemological laboratory can help assess identity and may comment on treatments when the evidence permits.
Origin and mining
Tanzanite is commercially associated with the Merelani Hills near Mount Kilimanjaro in Tanzania. The known mining area is geographically limited, which has shaped the gem’s reputation and supply. Mining can create economic opportunities but also raises questions about worker safety, land use, environmental management, and traceable sourcing.
Origin claims should be supported by documentation rather than inferred from color. Buyers interested in ethical sourcing can ask retailers about the supply chain, mining practices, and any independent records associated with the stone.
Identification and buying advice
Tanzanite can resemble other blue-violet gems, including sapphire, iolite, and some treated materials. Gemologists use refractive properties, pleochroism, spectroscopy, microscopy, and other tests to identify it. Color alone is not enough to establish species or origin.
Before buying, ask whether the gem has been heat-treated, whether it is natural zoisite, and whether any report is available. Compare color in more than one lighting environment and inspect the stone for visible inclusions, chips, and setting security.
Care
Tanzanite is less resistant to impact than sapphire and has cleavage, so protect it from knocks and sudden temperature changes. Clean gently with lukewarm water, mild soap, and a soft brush. Avoid ultrasonic and steam cleaners, and do not expose the gem to harsh chemicals or abrupt heating.
Remove tanzanite jewelry before sports, heavy work, or household tasks. Store it separately in a padded compartment, and ask a jeweler to check the setting periodically.
Frequently asked questions
Is tanzanite a separate mineral?
No. Tanzanite is the blue-violet gem variety of zoisite.
Where is tanzanite found?
Commercial tanzanite is associated with the Merelani Hills in northern Tanzania.
Is tanzanite usually treated?
Most jewelry tanzanite has been heat-treated to enhance blue-violet color. Sellers should disclose known treatments.
Can tanzanite be worn every day?
It can be worn carefully, but its cleavage and moderate hardness make it vulnerable to impact. Protective settings and gentle handling are recommended.
Sources
- Gemological Institute of America (GIA) — tanzanite properties and identification.
- Mindat.org — zoisite and tanzanite locality information.
- Handbook of Mineralogy — zoisite mineral data.