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Luster of Gems




Luster is the quality of reflected light from the surface of a gem or mineral and may vary somewhat in a single crystal.  For example, a crystal may have a vitreous luster on the surfaces parallel to its cleavage and have a pearly or silky luster perpendicular to the cleavage due to its fibrous nature. Gypsum is an example of this phenomenon. Luster is not a very useful diagnostic property in identifying such minerals.

Luster is divided into two basic types: metallic and non-metallic. There are also intermediate types called sub-metallic. Any gem or mineral that does not have a metallic appearance is described as non-metallic. Non-metallic gems and minerals are described in the following terms (listed in alphabetical order):

  • Adamantine - hard, steely brilliance like the reflection from a diamond (high index of refraction)
  • Chatoyant - Numerous hair-like inclusions aligned to produce "catseye" effect
  • Dull - Completly dull, eg. clays
  • Earthy (Dull) - Completly dull, eg. clays
  • Greasy - appears to be covered in oil or grease
  • Pearly - Formed by numerous partly-developed cleavages, eg. Pearls
  • Resinous - Luster of Resin, eg. Amber
  • Schiller - Caused by numerous platy inclusions or separations, eg. Sunstone
  • Silky - Noticeable, fibrous, shiney direction, eg. Satin Spar
  • Sub-Metallic - Almost metallic reflection, eg. Cuprite
  • Sub-Adamantine - Not quite adamantine in luster
  • Vitreous - Luster of broken glass (most gem minerals fall in this type), eg. Quartz
  • Waxy - Fairly dull luster, eg. wax

Terms of luster for metallic gems:

  • Metallic - Specular reflection, eg. Pyrite
  • Metallic-Dull - Has a dull metallic luster


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