4.26 ct. Usumbara Effect Tourmaline Cabochon
Color: Very Dark Green
Clarity: Transparent
Origin: Tanzania
Cut: Triangular Cabochon
Treatments: None
Measurements: 12.3 x 12 mm
A stone that is just so downright intriguing from a gemological perspective that we couldn't resist. These very particular Tourmalines display what is known as the Usumbara effect - a complex interaction of wavelength, width and color perception. This manifests itself what you see above: a deep ‘chrome’ green tourmaline that retains that color only up unto a certain width both in reflected and transmitted light. However, where the stone gets thick enough and the width passes a certain point, the transmitted color becomes pure red. It does require extremely strong light to see the effect, please excuse the fact we used our phone light in the pic above! This was a piece of unique rough that, despite the fact these are mostly overly dark and fractured, we just couldn’t help but have cut into a cab. An excellent overview and explanation of the effect is to be found here. Certainly not many of these to be had!