mineral

Blue Star Sapphire

Corundum (Al2O3)

Hardness: 9 on Mohs scale; Color: Blue with a milky sheen; Luster: Vitreous to sub-adamantine; Crystal Structure: Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.95-4.03.

Hardness: 9 on Mohs scale
Color: Blue with a milky sheen
Luster: Vitreous to sub-adamantine

Identified March 26, 2026More mineral →

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Physical properties

Hardness: 9 on Mohs scale; Color: Blue with a milky sheen; Luster: Vitreous to sub-adamantine; Crystal Structure: Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.95-4.03.

Formation & geological history

Formed in aluminum-rich metamorphic rocks (schists/gneisses) or igneous rocks (syenites/pegmatites). The star effect (asterism) is caused by needle-like inclusions of rutile aligned along the crystal axes.

Uses & applications

Primarily used in jewelry as a gemstone. Industrial corundum is used for abrasives and watch bearings, though high-quality star specimens are kept for collectors.

Geological facts

The star effect is most visible under a single direct light source like sunlight or a focused flashlight. The most famous example is the 'Star of India,' weighing 563 carats.

Field identification & locations

Identify by looking for a six-rayed star that moves across the surface as the stone is tilted. Commonly found in Sri Lanka (Ceylon), Myanmar (Burma), and Madagascar. Often found in alluvial 'gem gravel' deposits.