Mineral

Sapphire

Corundum (Al2O3)

Hardness: 9 on the Mohs scale; Color: Deep blue to violet-blue (shown); Luster: Vitreous; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 3.95–4.03.

Hardness: 9 on the Mohs scale
Color: Deep blue to violet-blue (shown)
Luster: Vitreous

Identified March 6, 2026More mineral →

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Physical properties

Hardness: 9 on the Mohs scale; Color: Deep blue to violet-blue (shown); Luster: Vitreous; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 3.95–4.03.

Formation & geological history

Formed in aluminum-rich igneous (pegmatites) or metamorphic rocks (marble/schist) under high pressure and temperature. Large, gem-quality sapphires are often found in secondary alluvial deposits.

Uses & applications

Primary use in high-end jewelry (faceted gemstones); industrial uses include infrared optical components, high-durability windows, and watch crystals due to extreme hardness.

Geological facts

Sapphire is the birthstone for September and the 45th anniversary gem. Any color of gem-quality corundum is called sapphire, except for red, which is classified as ruby.

Field identification & locations

Identify by its extreme hardness (scratches glass/steel easily) and characteristic pleochroism. Commonly found in Sri Lanka, Madagascar, Myanmar, and Montana (USA). Collectors look for clarity, color saturation, and the presence of 'silk' inclusions.