Luster of Minerals
The luster of a mineral has to do with the appearance and intensity of light that is reflected from its surface. A person who wants to determine the luster of a mineral specimen should use a good light source. Also, she/he should look at an unweathered surface of the specimen.First, the examiner
should decide whether the mineral’s luster is metallic or not. If it is nonmetallic, then he/she should decide which kind of nonmetallic luster the specimen has. Following is a list of types of luster:
metallic —looks like a piece of broken or polished metal. Examples are pyrite and galena.
submetallic — has a high luster that is transitional between that of broken metal and that of broken glass. An example is black sphalerite.
nonmetallic — does not look like metal.
Several kinds of nonmetallic luster are:
- adamantinehas extreme brilliance like a faceted diamond. Examples are diamond and red sphalerite.
- dull lacks glossiness and appears earthy like soil or clay. Examples are hematite and impure flint.
- greasy or waxy has a faint gloss like a coating of oil. An example is flint.
- resinous has a lustrous yelow or brown appearance like resin or tree pitch. Examples are yellow or brown sphalerite and sulfur.
- silky has the sheen of an aggregate of fibrous grains that have a parallel arrangement. An example is pickeringite.
- vitreous has a high luster like the surface of glass. An example is quartz.