Gems and Light Interaction

These flashcards cover key concepts related to how gems interact with light and the optical phenomena associated with gemstones.

Color

The most important contributing factor to a colored stone’s desirability, marketability, and value.

Selectivity Absorption

The process by which a gemstone absorbs some components of visible light and transmits others.

Iridescence

A rainbow effect created when light is broken up into spectral hues by thin layers.

Pleochroism

When a gem shows different body colors from different crystal directions.

Color Change

A distinct change in gem color under different types of lighting.

Fluorescence

Emission of visible light by a material when it’s stimulated by ultraviolet or X-ray radiation.

Chatoyancy

Bands of light in certain gems, caused by reflection of light from many parallel, needle-like inclusions or hollow tubes.

Asterism

Crossing of chatoyant bands, creating a star in the dome of a cabochon.

Band Theory

A theory that explains how an atom's outermost electrons transition from lower-energy valence bands to higher-energy conduction bands.

Dispersed Ions

Ions that cause color in gems by selectively absorbing light; examples include chromium and vanadium.

Intervalence Charge Transfer

A process where two transition elements with different valences exchange electrons to selectively absorb light.

Color Center

A small defect in the crystal structure of a material that can absorb light and give rise to a color.

Diffraction

A special kind of interference phenomenon that produces patches of pure spectral colors.

Adularescence

The cloudy bluish white light in moonstone, caused by scattering of light.

Charge Transfer

The movement of electrons back and forth between ions, causing the selective absorption of light.

Dispersion

The separation of white light into spectral colors.

Transition Elements

Elements that can selectively absorb some wavelengths of visible light and produce color in gems.