A star-shaped light pattern (often 4 or 6 rays) produced by oriented inclusions; typically visible on cabochon-cut stones and used as a descriptive/valuing feature.
Double refraction where light splits into two rays, sometimes producing doubled edges through transparent crystals; an optical clue tied to crystal structure.
A moving ‘cat’s‑eye’ band of light caused by aligned fibers or needle-like inclusions; commonly seen on cabochons and used to describe gemstone appearance.
Bands or patches of different color within one crystal caused by changing growth conditions or chemistry; reveals growth history and can affect appearance and value.
A visible glow under UV light (longwave/shortwave) caused by trace activators in the mineral; useful for identification and for evaluating fluorescent specimens.
A change in color or intensity when a crystal is viewed from different directions (often with polarized light); a diagnostic optical trait in some minerals and gems.
How much light passes through a specimen—transparent, translucent, or opaque—used for identification, grading, and deciding on lighting for display or photography.
