An Update on Color in
Gems. Part 3:
Colors Caused by Band Gaps and Physical Phenomena
Emmanuel Fristch
Gemological Institute of America
Santa Monica, California, USA
George R. Rossman
California Institute of Technolgy, Pasadena, CA, USA
Overview
This is the third part in a three-part series on the origin of color
in gem materials. This article is concerned with colors explained
by band theory, such as canary yellow diamonds, or by physical optics,
such as play-of-color in opal. In the case of band theory, the
color-causing entity is the very structure of the entire crystal: in
the case of physical phenomena, it is of microscopic dimension, but
considerably larger than the clusters of a few atoms previously
discussed..
Gems and Gemology 24, 81-102.