A very rare chrome green tourmaline with a textbook Usambara effect.
The Nchongo chrome tourmalines are a verdant green in both transmitted and reflected light. Once the thickness of the mineral reaches a critical point, dependant on concentration of the elements chromium and vanadium, the perceived color of the transmitted incandescent light suddenly shifts to red. This occurs viewing either the ordinary or the extraordinary ray at about the same thickness.
Pictures taken in daylight where the gem appears black, white LED light and incandescent light for the colour change.
Ideal for jewellery or as an addition to a collection.
