mineral

Blue Sapphire

Corundum (Al2O3)

Hardness: 9.0 on Mohs scale; Color: Deep blue (due to iron and titanium); Luster: Vitreous (glass-like); Crystal structure: Trigonal/Hexagonal; Cleavage: None (may show parting); Specific Gravity: 3.95-4.03

Hardness: 9
Color: Deep blue (due to iron and titanium)
Luster: Vitreous (glass-like)

Identified March 13, 2026More mineral →

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Physical properties

Formation & geological history

Formed in metamorphic rocks (schists, gneisses) and igneous rocks (syenites, pegmatites) rich in aluminum and poor in silica. Often found in secondary alluvial deposits (riverbeds). Can be millions of years old based on the host rock formation.

Uses & applications

Predominantly used as a gemstone in high-end jewelry. Industrial-grade sapphire (synthetic) is used for scratch-resistant watch crystals, surgical tools, and high-durability windows.

Geological facts

Sapphire is the second hardest natural mineral after diamond. While famous for blue, 'fancy sapphires' occur in every color except red (red corundum is classified as Ruby). The 'Star of India' is one of the most famous specimens in the world.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by steel or quartz) and high density. Commonly found in Sri Lanka, Madagascar, Kashmir, and Montana, USA. Collectors look for clarity, 'cornflower' blue saturation, and absence of inclusions.