mineral

Sapphire (Corundum)

Corundum (Al2O3)

Hardness: 9 on the Mohs scale. Color: Lavender/Blue. Luster: Vitreous (glassy) to Adamantine. Crystal System: Trigonal/Hexagonal. Cleavage: None (has parting). Specific Gravity: 3.95–4.10.

Hardness: 9 on the Mohs scale
Color: Lavender/Blue
Luster: Vitreous (glassy) to Adamantine

Identified April 12, 2026More mineral →

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Physical properties

Hardness: 9 on the Mohs scale. Color: Lavender/Blue. Luster: Vitreous (glassy) to Adamantine. Crystal System: Trigonal/Hexagonal. Cleavage: None (has parting). Specific Gravity: 3.95–4.10.

Formation & geological history

Formed in metamorphic rocks such as mica schists or gneisses, or in igneous rocks like syenites. They are frequently found in secondary alluvial (placer) deposits after being weathered out of their primary host rock over millions of years.

Uses & applications

High-quality transparent specimens are used as gemstones in jewelry. Industrial-grade corundum is used as an abrasive (emery) due to its extreme hardness, and for high-pressure windows or watch crystals.

Geological facts

Sapphire is the birthstone for September. Every color of the mineral corundum is called sapphire, except for red, which is uniquely classified as ruby.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by steel or quartz) and its high density (feels heavy for its size). Common locations include Sri Lanka, Madagascar, Myanmar, and Montana (USA).