mineral

Sapphire

Corundum (Al2O3)

Hardness: 9 on Mohs scale; Color: Deep blue; Luster: Vitreous to sub-adamantine; Crystal system: Trigonal; Specific gravity: 3.98-4.06

Hardness: 9 on Mohs scale
Color: Deep blue
Luster: Vitreous to sub-adamantine

Identified April 28, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Deep blue; Luster: Vitreous to sub-adamantine; Crystal system: Trigonal; Specific gravity: 3.98-4.06

Formation & geological history

Formed in igneous or metamorphic rocks like pegmatites, schists, or marbles when aluminum-rich magma cools or undergoes metamorphism without silica present. Commonly found in secondary alluvial deposits.

Uses & applications

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

Geological facts

Sapphire is the birthstone for September. While blue is most common, sapphires can occur in any color except red (which are Ruby). Some exhibit a star effect known as asterism.

Field identification & locations

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