Saturday, July 19, 2008
Another of my favourite colour change gems, Alexandrite. It was discovered in 1834 in the emerald mines of the Ural Mountains of Russia near the Tokovaya River. The discovery was made on the day of the coming of age of the future Tsar Alexander 11 so it was named for him and became the national stone ofRussia as it showed both red and green, the principal colours of Imperial Russia.
Russia has remained the primary source of Alexandrite but as the deposits were worked out, interest decreased. There were other mines but none of them produced stones with the colour change. In 1987, Alexandrites were discovered in Mina Gerais, Brazil. They showed a distinct colour change although the green is not as strong as Russian Alexandrites. Occasionally stones are found in Brazil with chatoyancy, the cat's eye effect, which has not been seen in Russian gems.
Top quality Alexandrite is rare and hardly used in modern jewellery. Tifany's gemmologist, George Kunz (1856-1932) was fascinated by the gem and the firm produced quality Alexandrite jewellery in platinum settings at the end of the 19th Century and early 20th Century. (Kunz had a beautiful pink/mauve gemstone named after him. Kunzite is on my wish list.)
Alexandrite has a hardness of 8.5. It's scarcity is due to its chemical composition. It is basically a crysoberyl but differs in that it not only contains iron and titanium but chromium as a major impurity which accounts for the colour change. Its formation requires specific geological conditions. The chemical elements beryllium (crysoberyl) and chromium (colouring agent) have contrasting chemical characteristics and are usually found in contrasting rock types. Not only
does Nature have to bring these contrasting rock types into contact with each other, but a lack of silica is also required to prevent the crystal from becoming an emerald. This geological scenario is rare and so is Alexandrite.
The colour change is spectacular. A vivid bluish green in daylight and a purplish-red in artificial light without a trace of brown or grey. This change will only occur on exposure to the different light surces. If a finely faceted stone obove one carat is indisputedly known to be of Russian origin then it will be rarer than ruby, sapphire or emerald and one of the most expensive gemstones in the world.
The Mystical Lore
It's considered a stone of very good omen.
In critical situations, it's supposed to help the wearer find new ways forward where logic won't provide an answer.
It's also reputed to aid creativity and inspire the imagination.