Tanzanite is the rich purplish-blue variety of the zoisite species*. Zoisite also comes in pink, green, yellow, and brown however, tanzanite is by far the most popular and well-known variety.
The zoisite species also contains massive varieties such as the translucent to opaque pink variety called thulite, which is often cut as cabochons. Another variety is green zoisite with ruby inclusions, which is used for sculptures and ornamental purposes.
Where can you find the tanzanite you need?
Pierres de Charmes carries a vast selection of fine quality tanzanite. Our collection of well-cut stones includes many different shapes and sizes.
Tanzanite Fact Sheet
Tanzanite has a vitreous luster with a relatively low hardness of 6.5 on the Mohs scale. As a result of its lower hardness, tanzanite jewellery should be stored and handled with care to avoid scratching.
Gemmologists can use many tools to identify tanzanite. Tanzanite displays strong pleochroism that can often be seen with the unaided eye however, a small portable instrument called a dichroscope can be used to see tanzanite’s diagnostic pleochroic colours. Tanzanite does not have any diagnostic inclusions but magnification can sometimes reveal internal fissures. Due to its low hardness, tanzanite in jewellery may show scratches and chips due to wear.
Rough tanzanite is often found as crystal fragments but can also present as well-shaped orthorhombic prisms with striated faces. Transparent material is facetted and more included translucent material can be fashioned as cabochons.
To date, the only known tanzanite deposit is in northern Tanzania near mount Kilimanjaro. This deposit was discovered in 1967.
Is tanzanite treated?
The blue colour of most tanzanite is the result of a relatively low temperature (400 -600°C) heat treatment. Many colours of zoisite will turn a purplish blue when heated and the treatment is stable. It should be noted that although many are treated in a lab some tanzanite could be altered by heat in their natural geological environments. Tanzanite can also be treated with a coating to enhance its colour. This treatment is easily detected with careful observation under the microscope.
Tanzanite in Jewellery
Tanzanite’s strong pleochroism means that it may appear to be different colours when viewed in different directions. For this reason the lapidary must be very careful to properly orient the stone to display the best colour. Tanzanite’s rich blue hues and rarity have made it very popular with jewellers and consumers alike. Its low hardness makes it best suited for pendants or earrings however it can be set in rings with settings that offer some protection. Tanzanite jewellery should be carefully handled and worn to avoid scratches and damage.
In 2002 tanzanite was officially named as a birthstone for the month of December and it is the gemstone for the 24th wedding anniversary.
Value and Quality Criteria
Colour is the most important quality criteria for tanzanite, the more rich and saturated the colour the higher the value. The most desirable colour is a rich blue with only a slight hint of violet reminiscent of fine sapphire. As mentioned above, when cutting tanzanite, the lapidary must be very careful to orient the stone so as to display the best colour making the quality of the cut a very important criteria for tanzanite. Larger stones tend to display more saturated colours and the size will have a direct impact on value. Like other gems, tanzanite will have a higher value when it has a higher clarity. Heavily included translucent material is often fashioned as cabochons.
Tiffany & Co. are to thank for the fact that tanzanite has become so well known in the short time since its discovery in 1967. The famous jewellery house became the primary distributor and launched an impressive marketing campaign that saw tanzanite’s popularity skyrocket making it one of the most sought after gems on the market today.
*In gemmology, as in nature, a species refers to a group with related members who share common features. In gemmology, the varieties or members of a species, share a common chemical composition of atoms organized in identical repeating patterns. In most cases the individual varieties are differentiated by the presence of small amounts of a chemical element that causes the particular colours associated with the different varieties.