RETURN TO INDEX OF ALL ARTICLES • RETURN TO LAPIDARY ARTS ARTICLES

LAPIDARY ARTS ARTICLE

The color of crystals
by MIKE BALDWIN

06.21.00: The color of a crystal can be its most striking feature. The causes of color are varied, and many minerals occur in a range of colors. Something looks a particular color largely due to your eye and brain reacting to different wavelengths of light. When white light (daylight) falls on a crystal, some of the wavelengths may be reflected, and some absorbed. If some are absorbed, those remaining will make up a color other than white because some of the wavelengths that make up white light are missing. Sometimes light is absorbed and re-emitted without changing and the mineral will appear colorless.

Idiochromatic: Some minerals are nearly always the same color because certain light-absorbing atoms are an essential part of their crystal structure. These minerals are described as idiochromatic. For example, copper minerals are nearly always red, green or blue according to the nature of the copper present.:

Allochromatic: A large number of minerals occur in a wide range of colors caused by impurities or light-absorbing defects in the atomic structure. For example, quartz, diamond, beryl, and corundum can be red, green, yellow, and blue. These minerals are described as allochromatic.

Play of colors: The color os some minerals is really a play of colors like that seen in an oil slick or a soap bubble. This may be produced when the light is affected by the physical structure of the crystals, such as twinning or cleavage planes, or by the development duirng growth of thin films. Microscopic "intergrowths" of plate-like inclusions also interfere with the light.