Pleochroism in Tanzanite

Tanzanite is famous for its remarkably robust trichroism, showing alternately blue, violet and burgundy relying on crystal orientation.

Tanzanite is the blue and violet number of the mineral zoisite (a calcium aluminium hydroxyl sorosilicate) belonging to the epidote group.

Tanzanite is a commerce identify that was first utilized by Tiffany and Firm for gem-high quality specimens of the mineral zoisite with a blue colour. Tiffany might have bought the fabric beneath the mineralogical identify of “blue zoisite,” however they thought the identify “tanzanite” would stimulate buyer curiosity and be simpler to market.

The identify “tanzanite” was given as a result of the world’s solely recognized tanzanite deposit of economic significance is in northern Tanzania. The identify displays the gem’s restricted geographic origin. The mines are all situated in an space of about eight sq. miles within the Merelani Hills, close to the bottom of Mount Kilimanjaro and the town of Arusha.


Gemmy Tanzanite from Merelani Hills (Mererani), Tanzania

Tanzanite’s Fascinating Shade

The mineral zoisite naturally happens in a variety of colours that embrace colorless, grey, yellow, brown, pink, inexperienced, blue, and violet. The identify “tanzanite” is used for a shade number of zoisite that ranges from blue to bluish purple to bluish violet. This kind of colour-selection identify shouldn’t be uncommon. The identify “ruby” is used for pink to barely purplish purple specimens of the mineral corundum; the identify “amethyst” is used for purple specimens of the mineral quartz; and, the identify “emerald” is used for inexperienced specimens of the mineral beryl. Every of those minerals happens in a variety of different colours. The blue colour of tanzanite is brought on by small quantities of vanadium inside the zoisite mineral construction.

Picture credit score: MIM Museum.

Pleochroism in Tanzanite

Tanzanite is a pleochroic gem. Pleochroism is a bodily property by which the fabric seems to be totally different colours when seen from totally different crystallographic instructions. Tanzanite is famous for its remarkably robust trichroism, showing alternately blue, violet and burgundy relying on crystal orientation.


Some specimens of tanzanite is usually a distinct blue when seen from one path, and differ from violet to purple when seen from different instructions. The group of three pictures on this web page exhibits a tanzanite crystal seen from three totally different crystallographic instructions. As a result of every of the three instructions reveals a unique shade, this makes tanzanite a “trichroic” materials.

Intense purple-pink tanzanite crystal


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