Andradite

History
This species of garnet was named after José Bonifácio de Andrade e Silva, an eminent Brazilian mineralogist of the 1800s. Andradite was little known until recent times except among collectors and gemstone devotees. At first, some specimens were found in a yellow colour. Then a new, green variety called demantoid was discovered in the Ural Mountains of Russia in 1868. The popularity of the gem rose rapidly, its novelty finding favour among prestigious jewellers. Production decreased after World War Two, and quality stones in suitable sizes reduced to a trickle.
It was only in the mid-1990s that an important source of demantoid was unearthed in Namibia, such that the stone promptly regained its share of the market.
Today, demantoid in fine quality commands the highest prices of all garnets.

 

Colour
Demantoid is the green variety of andradite garnet. Fine intense green colours with medium tones can very much rival emeralds and be easily mistaken for such. Andradite is also found in varying shades of yellow-green and yellow.
As with most gemstones displaying stunning green colours, demantoid andradite is coloured by traces of chromium in its chemical composition. Ferric ions also produce colour and sometimes yield interesting yellow stones.

 

Gemmological Properties
Some demantoid garnets feature an unusual property in the form of fine fibrous inclusions resembling a horse’s tail. Those particular demantoids are highly sought-after and this is one of the rare instances where inclusions can actually dramatically add value to a gemstone.
Andradite also possesses high dispersion – the ability to split light into the various colours of the spectrum. In fact, it performs this task even better than diamond, although darker colours can sometimes hinder the dispersive effect.

 

Mining Areas
Since the Namibian find, a new seam of demantoid andradite was discovered in Russia in 2002, enabling the country to reclaim its title of traditional fine-quality producer. A promising deposit was also found in Iran in 2001.