gemstone

Sapphire

Corundum (Al2O3)

Hardness: 9.0 on the Mohs scale. Color: Deep blue (cornflower to navy). Luster: Vitreous to adamantine. Crystal structure: Trigonal/Hexagonal. Cleavage: None (conchoidal fracture). Specific Gravity: 3.95-4.03.

Hardness: 9
Color: Deep blue (cornflower to navy)
Luster: Vitreous to adamantine

Identified July 3, 2026More gemstone →

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Physical properties

Formation & geological history

Formed in igneous or metamorphic environments such as pegmatites, basalt flows, or regional metamorphic rocks. Common in alluvial deposits where it survives weathering due to high hardness.

Uses & applications

Primarily used as a gemstone in fine jewelry. Industrial uses include watch crystals, high-durability windows, and abrasive compounds due to its extreme hardness.

Geological facts

Blue sapphires get their color from trace amounts of iron and titanium. Sapphire is the birthstone for September and has been a symbol of royalty, wisdom, and divine favor for centuries.

Field identification & locations

Look for high specific gravity (feels heavy for its size) and a characteristic waxy or glassy luster. In the field, look for hexagonal prismatic crystals. Major sources include Sri Lanka, Madagascar, Australia, and Myanmar.