gemstone

Ruby

Corundum (Al2O3:Cr)

Hardness of 9 on the Mohs scale, deep red to pinkish-red color due to chromium impurities, adamantine to vitreous luster, trigonal crystal system, no cleavage (parts by conchoidal fracture), specific gravity around 3.97-4.05.

Identified July 30, 2026More gemstone →

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Physical properties

Formation & geological history

Forms in metamorphic and igneous rocks, such as marble, basalt, and gneisses, where aluminum-rich rocks undergo high-temperature and high-pressure metamorphism. Found in alluvial placer deposits due to high weather resistance.

Uses & applications

Highly valued as a precious gemstone in fine jewelry, used in watch bearings, and historical applications in early lasers.

Geological facts

Ruby is one of the traditional cardinal gemstones. The red color is caused by trace amounts of the element chromium. High-quality natural rubies from Burma (Myanmar) are among the most expensive gemstones in the world, often surpassing diamonds in per-carat value.

Field identification & locations

Can be identified by its extreme hardness (scratches quartz and topaz), high density, and vibrant red fluorescence under UV light due to chromium. Common in East Africa, Southeast Asia, and parts of the Middle East.