This rarity among diamonds blushes in the heat
The magic of a living chameleon lies in its ability to change
color to hide from predators. In the gem world, a chameleon diamond
has no predators but many admirers. The magic is that it
changes color dramatically when heated and slowly reverts to
theoriginal color as it returns to room temperature.
This kind of diamond hydrogen-rich Type Ia (for a discussion
of diamond types, see Professional Jeweler, August 1999, p. 30)
is rare and desired mainly by collectors.
The charming characteristic would be lost in mounted jewelry,
and it would be a bad idea to approach the wearer with a Bunsen
burner, asking to witness her diamond changing hues. For the
jeweler, however, knowing about chameleons and wowing your customers
with amazing data about them can add to the romance of diamonds.
"Chameleons can go from their stable, generally grayish-green
color to a bright yellow," writes Dr. Emmanuel Fritsch in
The Nature of Diamonds (Cambridge University Press, Cambridge,
England, 1997). "Chameleon diamonds have unusually high
absorption bands at the red end of the visible spectrum (550
nanometers), causing the green stable color. This green color
is caused by hydrogen-containing defects."
Heating these diamonds at 200°-300°C (392°-572°F)
with an alcohol lamp causes changes in the absorption band. "Heating
the diamond or keeping it in the dark for an extended period
reduces the absorption, leaving the more saturated underlying
yellow visible," he says. The yellow is caused by nitrogen-related
color centers, he adds.
by Robert Weldon,G.G.