Description
This Chrome Green Tourmaline from Tanzania displays a very rare “Usambara effect” in this gemstone.
The blotchy red colour seen around the outer edges of this gemstone blends in nicely with the underlying green colour of this Chrome Green Tourmaline creating a very visually appealing two toned effect in this gemstone.
The “Usambara Effect” is rarely seen in gemstones and is named after the Usambara mountains in the Umba valley of Tanzania, a region where this effect was first observed and that has been a rich source of colour change and Usambara effect gemstones.
The Usambara effect has been observed in a number of gemstones including Chromium bearing Tourmaline and Garnets, Corundum, Epidote and Kornerupine.
Unlike colour change gemstones, the Usambara effect does not rely on changing the light sources used from a cool white light source to a warm incandescent light source to see the red or change in colour.
Instead the Usambara effect will appear as very attractive red areas around the outer edges of the gemstone, just by using a “Cool” white LED light source directed directly at the gemstone.
What should be of interest from a collectable gemstone point of view, is the “warm” red colour that is occurring from a “Cool” White LED light source in this green gemstone.
“Warm” reddish colours will normally occur with a “warm” incandescent light source.
So when we see these warm reddish colours occurring with a “cool” white light source, on an overall green gemstone it is doing the opposite or “Reverse” to what it is meant to be doing.
When this occurs in colour change gemstones, it is known as “Reverse” Colour Change and is very rare in colour change gemstones, making it very collectable indeed!
Apart from the amazing Usambara Effect this gemstone displays, this Chrome Green Tourmaline also glows red under Long wave UV Light and also when viewed through a Chelsea filter, this occurs as a result of the high chromium content found in this gemstone.
The Usambara effect is not something typically seen in gemstones, making them sought after curiosities of nature and highly appreciated by gem collectors, connoisseurs and gemmologists alike.
This gemstone weighs in at 1.56 cts is very well cut and is a very clean gemstone.
This stone is untreated and completely natural, it has a clarity rating of VVS – Very Very slightly included.
A videos of this gemstone stone displaying its impressive colour changes can be seen by clicking the video button below:
