mineral

Blue Sapphire

Corundum (Al2O3)

Hardness: 9 on Mohs scale; Color: Deep royal blue; Luster: Adamantine to vitreous; Crystal system: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.95–4.03.

Hardness: 9 on Mohs scale
Color: Deep royal blue
Luster: Adamantine to vitreous

Identified March 17, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Deep royal blue; Luster: Adamantine to vitreous; Crystal system: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.95–4.03.

Formation & geological history

Formed in aluminum-rich metamorphic rocks (schists/gneisses) or igneous rocks (alkali basalts/pegmatites) through high pressure and temperature. Found globally in deposits ranging from Precambrian to Cenozoic eras.

Uses & applications

Primary use is in high-end jewelry (rings, earrings, necklaces). Industrial-grade (synthetic or low-clarity) corundum is used for abrasives, watch crystals, and high-durability windows.

Geological facts

Sapphire is the birthstone for September and represents loyalty and nobility. It is the second hardest natural mineral on Earth after diamond. Famous examples include the 'Star of India'.

Field identification & locations

Field identification is based on high density and extreme hardness (ability to scratch glass and most other minerals). Commonly found in alluvial gravel deposits in locations like Sri Lanka, Madagascar, Myanmar, and Montana (USA).