The quality and quantity of light reflected from the surface of a gemstone. Luster depends on the refractive index and the polish or surface condition of the gemstone. The ability to take a good polish is much related to the hardness of a gemstone, hence gemstones with a large refractive index as well as a relatively high hardness have the highest luster. The mineral sphalerite is one of the exemptions to this rule as it has a low hardness of 3.5 on Moh’s scale but still has a subadamantine luster.
|Metallic||Metallic luster is the highest luster. Found on gems with a refractive index of 2.5 or higher. Equivalent to the polish on a metal object. Example: Hematite.
|Submetallic||Submetallic luster is slightly less lustrous than metallic.
|Adamantine||Adamantine luster is the luster exhibited by Diamonds and gems with a Refractive Index of 1.9 – 2.5.
|Subdamantine||Subadamantine luster is slightly less than that of a diamond. Example: Zircon.
|Vitreous||Vitreous is defined as a glass-like luster. Gems with a R.I from 1.3 – 1.8. Example: Moonstone can exhibit a Vitreous luster.
|Subvitreous||Subvitrious luster is somewhat less glass-like.
|Resinous||Resinous luster is that of a substance formed from resin. Example: Amber.
|Greasy||Greasy luster is seen on Serpentine.|
|Waxy||Waxy luster describes the luster observed on Jadeite and Nephrite.
|Dull||Dull luster describes the luster of Ivory.
Pearl Luster is defined by the sharpness and brightness of reflections as seen on the surface of a pearl. The Gemological Institute of America classifies pearl luster into five grades.
|Excellent||Reflections are uniformly bright and sharp.|
|Very Good||Slightly less defined, fairly sharp, bright reflections.|
|Good||Reflections are not clear but still fairly bright.|
|Fair||Reflections are very fuzzy and weak.|
|Poor||Reflections are non-existent or extremely weak.|