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.
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
- hard, steely brilliance like the reflection
from a diamond (high index of refraction)
- Numerous hair-like inclusions aligned to produce
- Completly dull, eg. clays
(Dull) - Completly dull, eg. clays
- appears to be covered in oil or grease
- Formed by numerous partly-developed cleavages, eg.
- Luster of Resin, eg. Amber
- Caused by numerous platy inclusions or
separations, eg. Sunstone
- Noticeable, fibrous, shiney direction, eg. Satin
- Almost metallic reflection, eg.
- Not quite adamantine in luster
- Luster of broken glass (most gem minerals
fall in this type), eg. Quartz
- Fairly dull luster, eg. wax
of luster for metallic gems:
- Specular reflection, eg. Pyrite
- Has a dull metallic luster