mineral

Sapphire

Corundum (Al2O3)

Hardness: 9 on Mohs scale. Color: Deep blue (likely due to Iron and Titanium). Luster: Vitreous (glassy). Crystal structure: Trigonal/Hexagonal. Cleavage: None. Specific gravity: 3.98-4.06.

Hardness: 9 on Mohs scale
Color: Deep blue (likely due to Iron and Titanium)
Luster: Vitreous (glassy)

Identified June 17, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale. Color: Deep blue (likely due to Iron and Titanium). Luster: Vitreous (glassy). Crystal structure: Trigonal/Hexagonal. Cleavage: None. Specific gravity: 3.98-4.06.

Formation & geological history

Formed in aluminum-rich metamorphic rocks (schist, gneiss) or igneous rocks (syenite, pegmatite) during high-pressure cooling. Often found in secondary alluvial deposits.

Uses & applications

Primarily used in high-end jewelry as a gemstone and as a birthstone for September. Industrial uses include scratch-resistant watch crystals and scientific instruments.

Geological facts

Corundum is the second hardest natural mineral after diamond. Red corundum is called ruby, while all other colors are classified as sapphires.

Field identification & locations

Identify by its extreme hardness and high density. Commonly found in locations like Sri Lanka, Myanmar, Australia, and Thailand. Check for clarity and color saturation under magnification.