Definition of "pleochroism" [ple•och•ro•ism]

• The property possessed by some crystals of exhibiting different colors, especially three different colors, when viewed along different axes. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Such an effect is called pleochroism, and crystals which show variations in their colour when viewed from different angles, or by transmitted light, are called pleochroic, or pleochromatic -- from two Greek words signifying "to colour more.""
• "Iceland-spar is extensively used in the construction of Nicol's prisms for polariscopes, polarizing microscopes and saccharimeters, and of dichroscopes for testing the pleochroism of gem-stones."
• "Biotite, containing haloes, 223; pleochroism of, 235; intensified pleochroism in halo, 235."