New Mexico Mineral Symposium — Abstracts

In the last 20 years scientists have been successful in explaining what causes color in a number of minerals and gems.

The results of the work of people like Nassau, Rossman, Fristch, Loeffler, and others reveal that minerals can generally be categorized into five major groups related to their color cause. These groups are:

PHYSICAL OPTICS - minerals whose color is due to physical rather than chemical phenomenon;

DISPERSED METAL IONS - one of the transition
metals creates a color condition;

CHARGE TRANSFER - Electrons move from one atom to another by absorbing light energy;

BAND GAP - Metals and some compounds in which energy is absorbed in the gap between a substance's Fermi Surface and absorption band;

COLOR CENTERS - Some external force, such as heat, radiation,
etc., disturbs the internal structure creating a condition under which light energy is absorbed.

This talk, supplemented with color slides, will describe the specific causes of color in a number of popular minerals ranging from gold through the rare sulfosalts, quartzes, pegmatite gems, and a host of collected minerals.