Luster is referred to the light reflected from the surface of gems. In some gemstones, there is internal light reflections also such as facet stones with transparency. However internal reflection of light is not called luster. It is called brilliance. Luster is the way a mineral either shines or does not shine. Gems and minerals can have metallic and non metallic luster.
Various terminology are used for defining luster for a gemstones. Such as Adamant, Vitreous, Silky, Greasy etc. Normally luster can be defined in two categories:-
- Metallic (such as pyrite , hematite)
- Non Metallic (all gemstones)
One will get in gemstones most non metallic gemstones. Following are described brief description of each luster type:;-
- Sub Adamantine
- Sub Vitreous
|Resinous||Like resins, such as tree sap|
|Silky||Soft-looking with long fibers|
Adamantine is highest form of luster just like mirror. Its best example is Diamond.
Some gemstones has luster like diamond but they are not fully adamantine. However they are closed to adamatine. They somes in sub-adamantine category. Their examples are Cubic Zircon.
Some gemstones have glassy like shining on surface such as tourmaline, Quartz, topaz. The majority of gems show a vitreous luster. Examples are beryl, quartz, topaz, ruby, emerald and others with refractive indices between 1.50 and 1.70.
In sub vitreous, the gemstones are included which have low reflection of light on surface such as flourite.
Gems with greasy surface will have oil like or fat like. The example is serpentine. Another example is garnet or peridot. These luster are characteristic of those polished surfaces that are not perfectly flat but that approach flatness.
The gemstones with silky luster will be based on having some fibrous material such as Gypsum and Malachite. Another example is Ulexite or moonstone. They look like having texture of fabric. Polished tiger’s eye shows a vitreous luster on its surface, overlaying a fibrous body.
Some gemstones have orient luster which is called Pearly. They show an iridescent play of colors on their surfaces.
Amber are consisted of preserved prehistoric plant resign. This gemstone have resinous luster example in best. Sphalerite has also resinous luster. The gem materials that are soft and have low refractive indices, like Amber and Opal.
Some gemstones looks like having kind of a wax on surface. Best example is turquoise and Opals
As this is shown by name that gemstone with having dull luster will be reflect very very low light. Dull will have fine grain like surface.
Some gemstones or minerals have metallic matters in them. Such as Pyrite and Hematite. Though
they are not used as gemstones in general however in some cases, they are.