Tanzanite

Tanzanite is a gorgeous blue and purple mineral found in Tanzania. It is only found in a very small area and is quite an interesting mineral, displaying strong trichroism.

This means it may appear to be different colours at different angles, and under different types of light.

Almost all of the Tanzanite available on the market is heat treated, as naturally it occurs in a reddish brown colour, and requires heat treatment to bring out the blue-violet colours.

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Appearance, Uses and History

Tanzanite was introduced to the market in the 1960s by Tiffany & Co. It was, of course, named after Tanzania, the country of its discovery.

It is a form of zoisite, but ‘blue zoisite’ was not considered to be ‘marketing friendly’, as the company considered that it sounds a little like ‘suicide’. Whether that is true or not – honestly, no way of being sure.

The rather unique conditions which led to the formation of Tanzanite means it is extremely unlikely to be found anywhere else on earth. The area where it is found is only four kilometres wide and two kilometres long.

In 2002, the American Gem Trade Association made Tanzanite a new birthstone for December, the first change to this list for ninety years.

Like most coloured gemstones, the clarity, colour, cut, and carat weight ultimately determines the value of a piece of Tanzanite. During 2012, 54 tons of Tanzanite was produced, with projections showing a similar output can continue for 23 years.

Tanzania has imposed an export ban of rough Tanzanite specimens of over 1 gram, in order to aid local gem cutting and lapidary industries, as well as encouraging the private sector to train lapidarist’s, gem cutters, and jewellers.

In an attempt to combat corruption and smuggling of minerals, Tanzania enacted new laws in 2010 and 2017 to impose higher taxes on the mineral export industries and make it mandatory for the government to have a stake in all new mining projects. This has, unfortunately, slowed investment in the sector. 

Locales

Tanzanite occurs in only a single locale worldwide, the Lelatema Mountains in the Manyara Region of Tanzania.

Mineralogy

Chemistry
Tanzanite is a gemstone quality form of Zoisite, with the formula {Ca2}{Al3}(Si2O7)(SiO4)O(OH).
Colours and Variations
Many are typically a brown or pale grey colour, with heat treatment used to produce a strong purple-blue colour.
Streak
White or colourless
Luster
Vitreous
Fracture
Uneven to conchoidal
Transparency
Transparent to translucent.
Crystal habit
Prismatic crystals, massive, columnar. Crystals often show striations, but not always.
Mohs hardness
6.5
Specific Gravity
3.10 – 3.38
Fluorescence
Seems to appear a stronger blue.
Easiest testing method
Tanzanite is strongly pleochroic, showing different colours from different angles. It is also trichroic, as it can be viewed from three directions, each with a different colour.
However, synthetic imitations exist; proper gemological inspection is recommended.
Common Treatments
Very often heat treated to around 400-500 degrees to enhance colouration.

Hazards and Warnings

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis.

When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Arabic:

  • تنزانيت

Hindi:

Portuguese:

Bengali:

Indonesian:

Punjabi:

English:

Italian:

Russian:

  • Танзанит

French:

Japanese:

  • タンザナイト

Spanish:

  • Tanzanita

German:

  • Tansanit
  • Tanzanit

Korean:

  • 탄자나이트

Thai:

Gujurati:

  • તાંઝાનાઇટ

Mandarin and Traditional Chinese:

  • 坦桑石

Urdu:

Further Reading / External Links