Usambara effect Chrome Tourmaline crystal. Tanzania. 13.96 carats.

Product Code: TRUS11
Units in Stock: 1
A dark green crystal of Usambara effect Chrome Tourmaline from Nchongo, Umba Valley, Tanzania.

The Usumbara effect first came to attention in 1997 on the discovery of Chrome Tourmalines which exhibited a unique phenomenon. In normal lighting conditions, daylight or incandescent, reflected or transmitted, these crystals appear a very dark green colour.

However, when a directed light source such as a penlight is transmitted through the stone, the thickest portion in the correct orientation appears a bright red colour, as demonstrated in image 4.

This unique effect is not the same optical phenomenon as the colour change seen in Alexandrite or some Garnets, but is the light absorption properties of Chromium and Vanadium affecting our eyes perception of colour during the passage of light through the crystal.

Gem quality crystals such as this one are becoming increasingly rare.

weight:  13.96 carats
shape:   Rough crystal segment
dimensions:  19.91 x 14.18 x 7.98 mm
treatment:  None