Phenomenon · Reviewed definition

Asterism

An optical phenomenon in which two or more bright bands intersect to form a star-like pattern, commonly from oriented internal features in a cabochon.[1]

Also known as: Star Effect

Plain English

What it means

Asterism is the star effect seen in certain gems.

Why it matters

Its geometry can reflect organized internal features and crystal orientation.

What it does not tell you

Not every apparent star has the same cause or diagnostic value.

Evidence

References

  1. 1
    Structures Behind the Spectacle: Optical Effects in Phenomenal Gemstones

    Gemological Institute of America

    Open source