gemstone

Blue sapphire

Corundum (Al₂O₃), blue variety colored mainly by iron and titanium

AI-generated identification · may be incorrect

Deep blue, transparent, faceted oval; vitreous luster and trigonal crystal structure. Hardness 9 on the Mohs scale; cleavage is absent, with imperfect parting. The photograph alone cannot establish whether it is natural, synthetic, or treated.

Identified October 5, 2026More gemstone →

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Physical properties

Formation & geological history

Forms in aluminum-rich, silica-poor rocks and in metamorphic settings; gems are also recovered from river gravels. Sapphire deposits span many geological ages.

Uses & applications

Used in jewelry and, because of its hardness, in specialty windows, watch crystals, and technical components.

Geological facts

Sapphire is the non-red gem variety of corundum; red corundum is called ruby. Heat treatment is common in the gem trade.

Field identification & locations

Look for strong hardness, high luster, and blue color, but identification and natural-versus-synthetic status require gemological testing. Major sources include Sri Lanka, Madagascar, Myanmar, Australia, and Montana, USA.