Birthstone Guide: Tanzanite for Those Born in December

Looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers the December birthstone tanzanite and how this relatively new gemstone compares to its purple and blue-hued rivals.

In the grand scheme of gemstones and their history, tanzanite, a variety of zoisite, is a relative newcomer to the market. It was discovered in 1967 in Tanzania, from which the gemstone’s name was derived, and was first brought to the Western market by Campbell Bridges.

Tanzanite GemA HM
A faceted and polished tanzanite photographed by Henry Mesa.

Known and valued for its intense purple-blue colouration, tanzanite has enjoyed a steady popularity within the jewellery trade since the US company Tiffany’s started selling it in 1968.

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It can be transparent to translucent with varying colour saturation. One of the initial slogans related to Tanzanite was the fact that you could find it only “in Tanzania and Tiffany’s” because the only known locality for tanzanite even today is in Tanzania.

Tanzanite Crystals and Treatment

Tanzanite is often found as broken fragments, but when well-formed, the crystals are beautiful. They are prismatic with a rectangular cross-section and can have striations running parallel to the length of the crystal.

Often, tanzanite is heat treated to enhance the desired purplish-blue colour. It is a strongly pleochroic gemstone that can look purple when viewed in one direction and blue when viewed in another.

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It is a trichroic gemstone when unheated, meaning you can see three distinct colours: blue, yellow and pinkish purple. When heated, the yellow is eliminated, leaving you with a dichroic gemstone displaying blue and violet. These colours can be seen when using a dichroscope.

Tanzanite Pleochroism Polaroid LightTop: the three distinct colours of the trichroic gemstone tanzanite (only two colours can be viewed in any one direction).
Bottom: Changing the orientation of polarised light by 90-degrees allows for different colours to be observed in tanzanite.

Tanzanite Care and Caution

Tanzanite has a hardness of 6.5 on the Mohs scale, which is relatively not that hard. It is susceptible to scratches, abrasions and bruises.

This gemstone is also, unfortunately, a material with low durability, making it brittle. It can chip and fracture easily, so great care it needed when wearing it.

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Taking these factors into consideration, tanzanite is best worn in jewellery that is either for occasional wear, or set into earrings and necklaces to protect it from the possibility of being knocked or damaged when set in a ring. Avoiding ultrasonic cleaners and excess heat is also advisable.

Tanzanite Fracture from Ultrasonic Cleaner 8220 PDA fracture in tanzanite caused by an ultrasonic cleaner. Photographed by Pat Daly.

As one of the two birthstones for December, the second being turquoise, tanzanite is a gemstone worthy of a special occasion, such as a birthday, for wearing with pride.

Read more about the history, mythology and uses of turquoise here.

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Cover image: A tanzanite crystal from the Gem-A Gemstone and Mineral Collection. Photographed by Henry Mesa.