What is Luster?
Luster is a term used to describe the overall sheen of a mineral’s surface. The sheen of a mineral may be similar to that of a polished metal as well as that of a metal that is unpolished and pitted by tear and wear. Minerals may also have sheens similar to glass or earthy, dull appearances. Luster does not imply the color of a mineral. For instance, crystals of brass-yellow pyrite have metallic luster. This luster is also found in crystals of shiny grey galena. The luster of quartz minerals is said to be vitreous or glassy even though this mineral occurs in varied colors including rose, purple, yellow and another wide range of hue. A mineral’s luster is determined by the way its substance reflects light. Luster is one of the main properties that mineralogists use in determining a mineral’s identity.
The Varying Kinds of Luster
There are numerous mineral categories in the earth. As one of the properties in minerals, there are different types of luster as there are different mineral categories. Luster is divided into two categories namely nonmetallic and metallic. Metallic minerals tend to have a shiny and opaque appearance. There are various sub-categories of luster in nonmetallic minerals. Metallic luster occurs on reflective and opaque minerals that have an appearance similar to that in polished metal. Some minerals with metallic luster include pyrites that are used in coins, copper and gold nuggets. Minerals that have a submetallic luster mostly resemble metals though have a dull or less reflective appearance due to corrosion and weathering. Such include cinnabar and sphalerite. There are minerals that have a completely nonmetallic luster. Thus type of luster gives minerals a nonmetallic appearance. An example of nonmetallic luster is adamantine, a type of luster where a mineral has a brilliant, shiny appearance with a hard diamond look. Such minerals may be translucent or transparent and include cubic zirconia and diamonds.