corundumbearing

Corundumbearing is a geological term used to describe rocks or mineral assemblages in which corundum, the mineral form of aluminum oxide (Al2O3), occurs as a significant constituent. Corundum is notable for its hardness (9 on the Mohs scale) and for its gem varieties—ruby (red) and sapphire (any color other than red)—though in most rocks corundum appears as opaque, coarse grains or as inclusions.

Occurrence and formation: Corundum forms under high-temperature and high-pressure conditions in aluminous rocks. In metamorphic terranes with abundant aluminum, corundum crystallizes during granulite- or amphibolite-facies metamorphism. It can also occur in marble and quartzite suites derived from impure limestone or clay-rich protoliths. Corundum may appear as coarse grains, bands, or disseminations and often survives weathering as detrital grains that can accumulate in alluvial placers.

Economic significance: Gems: large, clear crystals of corundum with desirable color can be gem-quality ruby, sapphire, or related varieties. Abundant corundum in a rock is usually not a direct indicator of gem quality, but provenance studies of rubies and sapphires frequently rely on corundum-bearing rocks as potential source rocks.

Industrial use: Corundum is extremely hard and abrasion resistant, used as an abrasive material and in cutting tools. In geology, the presence of corundum can affect the physical and chemical behavior of rocks at high-grade metamorphism.

Detrital occurrence: Corundum’s resistance to weathering makes detrital grains common in sedimentary and placer deposits, where they may be mined for gemstones or industrial use.