mineral

Blue Sapphire

Corundum (Al2O3 - Aluminum Oxide with Iron and Titanium impurities)

Hardness: 9 on the Mohs scale (second only to diamond); Color: Deep velvet blue; Luster: Vitreous (glassy); Crystal Structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific Gravity: 3.95 - 4.03.

Hardness: 9 on the Mohs scale (second only to diamond)
Color: Deep velvet blue
Luster: Vitreous (glassy)

Identified March 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed in metamorphic rocks such as marble and schist, or igneous rocks like basalt. Blue coloration comes from traces of titanium and iron. They occur across diverse geological ages, primarily in alluvial deposits or primary rock veins.

Uses & applications

Predominantly used as a precious gemstone in high-end jewelry (rings, bracelets, necklaces). Industrial-grade corundum is used as an abrasive or in scratch-resistant watches and windows.

Geological facts

Sapphires are one of the 'Big Four' precious gemstones. The deep blue color shown in the image is often referred to as 'Royal Blue' or 'Midnight Blue.' Historically, sapphires were thought to protect royalty from envy and harm.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by quartz or steel) and high density. Commonly found in Sri Lanka, Madagascar, Australia (often very dark blue/black), and Thailand. Collectors look for clarity, saturation of color, and 'silk' inclusions.

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