Luster is a term associated with many different things, but we usually think of the connotation as a means of defining beauty of some sort. However, when it comes to gemstones specifically, luster actually has a specific meaning, and you can use it to better determine which gemstone may be right for you or someone close to you. Scientifically speaking, luster refers to the shine a stone gives off when light is reflected off of it. Luster also refers to mineral stones as well, at which point it is divided into metallic and non-metallic. Non-metallic lusters include minerals that are dull, greasy, or resinous, among other things. As far as gemstones are concerned, the majority of them are classified as having non-metallic lusters, if only because they rarely fit the metallic category, or the submetallic subcategory.
Luster Descriptions For Gemstones
- Vitreous is the term used to refer to non-metallic glassy luster, like most gemstones have. You can see this vitreous characteristic in Sapphire, Spinel, Quartz and similar minerals.
- Pearly is another luster type that is often associated with certain types of gemstones, and you can see this aesthetic quality in the mineral talc.
- Greasy, which looks as though a coating of oil or fat is over the mineral (graphite).
- Adamantine which is a highly reflective mirror like aesthetic (diamonds).
- Dull, which refers to minerals that have little to no luster of their own because they scatter light in all directions.
Needless to say, dull luster minerals are rarely used for jewelry. One of the more interesting luster types is silky, which refers to minerals that have parallel fibers, similar to the texture of silk fabric.
However, it is important to note that few gemstones exhibit one particular luster, because luster can change depending on which face of the gemstone is being viewed. Luster is a light phenomenon, caused by the way light hits a specific area of the gemstone. That said, if the gemstone is not uniform on every face, it will likely not display the same luster on every face. Gypsum is one such gemstone that can exhibit several different lusters, thanks to the many different aggregations it has before refinement. One side could be reflective, while another could be silky, and yet one side could still be dull.
Because luster can change on different faces of non-uniform gemstones, the vast majority of gemstones used in jewelry are cut and molded to be uniform across all sides, or at least in a manner that exhibits the same luster from any viewing angle. After all, no one wants a diamond that is only adamantine on one side and none of the others.
In the end, though luster is an important part of identifying the qualities of various gemstones, it is not always useful or effective, thanks to the fact that gemstones can exhibit many different lusters. This makes it rather pointless to classify a gemstone by luster, at least until it had been refined.
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