mineral
Raw Ruby (Corundum)
Corundum (Aluminum Oxide, Al2O3)
Mohs hardness of 9.0; color range from pinkish-red to deep pigeon-blood red; vitreous to adamantine luster; hexagonal (trigonal) crystal system; no true cleavage but shows parting.
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Physical properties
Mohs hardness of 9.0; color range from pinkish-red to deep pigeon-blood red; vitreous to adamantine luster; hexagonal (trigonal) crystal system; no true cleavage but shows parting.
Formation & geological history
Formed via regional or contact metamorphism of aluminum-rich rocks (shales, limestones) or in igneous environments such as syenites. Found in marble deposits and alluvial gravels.
Uses & applications
Used primarily in jewelry as a precious gemstone; industrial grades are used for abrasives, watch bearings, and laser production.
Geological facts
Ruby is the red variety of corundum; all other colors are called sapphire. It is the second hardest natural mineral after diamond. Some rubies exhibit asterism (the star effect) when cut as cabochons.
Field identification & locations
Identified in the field by its extreme hardness (will scratch glass and quartz easily) and its hexagonal barrel-shaped crystal habit. Common in Myanmar, Sri Lanka, Madagascar, and East Africa.
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