Luster is a description of the way a mineral surface looks when light reflects off of the surface.
Luster has two categories, metallic and nonmetallic.
Metallic Luster refers to minerals that look like a shiny metal.
Examples include galena, pyrite, magnetite, and some varieties of hematite.
Nonmetallic Luster. There are a number of different nonmetallic lusters.
A. Vitreous. Also called glassy. Examples include quartz and tourmaline.
B. Resinous. Minerals that look like resin (a little bit like the look of plastic). Examples include sulfur and sphalerite.
C. Pearly. Minerals with a pearl-like, iridescent luster. Talc is a good example.
D. Greasy. Some minerals look like they have a thin layer of oil on them. Graphite is the best example.
E. Silky. Minerals that look like fibers of silk. Fibrous gypsum and malachite have this luster.
F. Adamantine. This describes minerals with a brilliant luster, sometimes with colors flashing in the mineral.
Diamond is the best example. Some clear lead minerals, like cerussite and anglesite, also have adamantine luster.