from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The property possessed by some crystals of exhibiting different colors, especially three different colors, when viewed along different axes.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The optical phenomenon in some colored, transparent crystals (such as tourmaline) in which the color is different in different directions.
from the GNU version of the Collaborative International Dictionary of English
- n. The property possessed by some crystals, of showing different colors when viewed in the direction of different axes.
from The Century Dictionary and Cyclopedia
- n. In crystallography, the variation in color observed in some crystals when viewed in different directions, due to the fact that the rays having vibrations in different planes suffer absorption in different degrees.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the phenomenon of different colors appearing when certain crystals are viewed from different directions
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.
Because of Iolite's pleochroism (it appears a different color depending on the angle of the light), they could look through the mineral to determine the sun's exact position and navigate accurately.