From Chatoyancy to Fluorescence: Exploring The Optical Effects of Gemstones

Gemstones captivate us not only with their colors but also with their fascinating optical effects. These effects which are caused by the interaction of light with the stone’s structure, add an extra layer of beauty and intrigue to each specimen.

Chatoyancy (Cat’s Eye Effect)

tigers eye gemstone

This effect occurs when light reflects off parallel inclusions within a gemstone, creating a single bright band of light that appears to move across the surface.

Other stones that demonstrate chatoyancy:

  • Hawk’s Eye: A blue variant of Tiger’s Eye.
  • Pietersite: Contains fibrous inclusions that produce a similar effect.
  • Silkstone: A type of quartz with fine parallel inclusions.
  • Actinolite: Can display chatoyancy when cut properly

Asterism (Star Effect)

star ruby
Star Ruby with a six-ray star

Some stones, like star sapphires and rubies, display a star-like pattern due to the reflection of light from needle-like inclusions oriented in specific directions.

Other stones that demonstrate asterism:

  • Star Sapphire: Known for its distinct star pattern, typically with six rays.
  • Star Garnet: Usually found in reddish hues, with four or six-ray stars.
  • Star Rose Quartz: Exhibits a soft pink color with a star effect.
  • Black Star Diopside: Typically displays a four-ray star, with a striking black color.

Read more: Stones and Stars: 5 Gemstones with Captivating Asterism Effects


Moonstone with it’s famous adularescence (image: firegemshub)

Moonstones exhibit a soft, billowy light that seems to float within the gem. This effect is caused by the scattering of light within the stone’s layered structure.

Other stones that demonstrate adularescence:

  • Labradorite: While primarily known for labradorescence, some specimens can also show adularescence.
  • Peristerite: A variety of albite feldspar showing a bluish adularescent sheen.


labradorescence of Labradorite
The labradorescence of Labradorite (image: Martin Heigan/cc)

Labradorite showcases a remarkable play of colors, from blues to greens and even oranges. This effect is due to the interference of light within the stone’s internal layers.

Other stones that demonstrate labradorescence:

  • Spectrolite: A high-quality variety of labradorite from Finland, displaying vibrant and full-spectrum colors.
  • Andesine-Labradorite: A feldspar mineral that can show a mix of labradorescence and aventurescence.


Seen in gems like opal and ammolite, this effect produces a rainbow-like play of colors as light diffracts through the stone’s microstructure.

Other stones that demonstrate iridescence:

  • Mother-of-Pearl (Nacre): Found inside mollusk shells, exhibiting a pearly luster with iridescent colors.
  • Fire Agate: Displays a swirling, fiery iridescence due to its layered structure.
  • Titanium-treated Quartz: Quartz crystals coated with titanium to produce a vivid iridescent effect.


color changing gemstones

Stones like tanzanite and alexandrite exhibit different colors when viewed from different angles, caused by the stone’s ability to absorb light differently along various crystal axes.

Other stones that demonstrate pleochroism:

  • Iolite: Also known as cordierite, it can show shades of violet, blue, and gray.
  • Kunzite: Exhibits varying shades of pink to violet when viewed from different angles.
  • Andalusite: Displays colors like green, yellow, and red-brown depending on the angle of light.


Certain gemstones, such as diamonds and rubies, can glow under ultraviolet light due to impurities within the stone.

Other stones that demonstrate fluorescence:

  • Fluorite: Known for a wide range of fluorescent colors, including blue, green, and purple.
  • Scapolite: Exhibits a yellow or orange fluorescence.
  • Calcite: Can fluoresce in various colors, including red, blue, and green.

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