Luster describes the general appearance of a mineral’s surface areas in reflected light. Several classes highlight a mineral’s luster, as follows:
This is the look and reflectivity of an untarnished metal surface. In addition, “submetallic” means slightly less than metallic. Minerals with a metallic luster are many and include antimony, arsenic, bornite, bournonite, chalcopyrite, cobaltite, copper, cuprite, enargite, galena, gold, hematite, iron, magnetite, pyrite, silver, skutterudite, sperrylite, and uraninite.
This term simply means glassy. In addition, “subvitreous” means slightly less than glassy. Minerals with a vitreous luster are also many and include adamite, azurite, barite, benitoite, beryl, corundum, diopside, dolomite, elbaite, euclase, fluorite, grossular, hemimorphite, lazurite, rhodochrosite, smithsonite, sodalite, spessartine, and spinel.
This refers to the sparkling luster of a diamond. In addition, “subadamantine” means slightly less than that sparkling. Minerals with an adamantine luster include anatase, cassiterite, cerussite, cinnabar, diamond, proustite, pyrargyrite, rutile, and wulfenite.
Resinous simply refers to having the luster of a piece of resin. Minerals with a resinous luster include anglesite, mimetite, monazite, orpiment, pyromorphite, scheelite, and zincite.
This class refers to a luster like that of a pearl or mother-of-pearl. Minerals with a pearly luster include diaspore, gibbsite, margarite, muscovite, and talc.
Minerals with a greasy luster appear to be coated with a thin layer of oil. Minerals with a greasy luster include antigorite, carnallite, cryolite, descloizite, gadolinite, nepheline, pyrophyllite, sulfur, and xenotime.
This class refers to minerals that appear to have a wax-like coating. Minerals with a waxy luster include brucite, chrysocolla, opal, turquoise, and varisicite.
Minerals with a silky luster appear much like the surface of a piece of silk or satin. Minerals with a silky luster include aurichalcite, chrysotile, dumortierite, malachite, pectolite, riebeckite, sillimanite, and ulexite.
This refers to minerals whose surfaces produce little or no reflection. This class includes boracite, borax, carnotite, chlorargyrite, clinochlore, erythrite, goethite, maghemite, montmorillonite, and purpurite.
Minerals with an earthy luster have the nonlustrous appearance of raw earth. They include annabergite, kaolinite, palygorskite, pyrolusite, and stibiconite.
All specimens from the David J. Eicher Mineral Collection; images © David J. Eicher