Definition

Noun: - The optical phenomenon in which a substance appears to be different colors when viewed from different directions, especially under polarized light: This property is observed in certain anisotropic crystals, where light is absorbed differently depending on the direction of its vibration relative to the crystal's axes.

Usage and Examples

• General Usage:
  • The gemologist identified the mineral by its strong pleochroism, noting it appeared blue from one angle and green from another.
  • Pleochroism is a key diagnostic feature for distinguishing between similar minerals in thin-section analysis.
• Scientific Context:
  • In optical mineralogy, pleochroism is used to determine the crystallographic orientation of a sample.
  • The study of pleochroism helps in understanding the atomic structure and bonding within crystals.

Advanced Usage and Concepts

• Dichroism vs. Pleochroism: While pleochroism is the general term for showing two or more colors, specifically refers to the property of showing two colors. Pleochroism is the broader category.
• Pleochroic Halo: A microscopic, colored ring seen in some minerals (like biotite) surrounding radioactive inclusions, caused by radiation damage that alters the mineral's pleochroic properties.

Variants and Related Words

• Pleochroic (adjective): Exhibiting pleochroism.
  • The tourmaline crystal was distinctly pleochroic.
• Pleochromatism (noun): A synonym for pleochroism, though less commonly used.

Synonyms

• Color variation (general, non-technical)
• Dichroism (specific, for two colors)
• Trichroism (specific, for three colors)

Antonyms

• Isotropy: The property of being identical in all directions; non-pleochroic materials are isotropic with respect to light absorption.

Related Phrases and Terms

• Absorption pleochroism: The type of pleochroism caused by differential absorption of light waves.
• Pleochroic scheme: The specific set of colors exhibited by a pleochroic mineral.

Noun

1. the phenomenon of different colors appearing when certain crystals are viewed from different directions