gemstone

Blue Sapphire

Corundum (Al2O3)

Hardness: 9 on the Mohs scale. Color: Deep royal blue. Luster: Vitreous (glass-like). Crystal Structure: Trigonal. Specific Gravity: 3.95–4.03. Cleavage: None (has parting).

Hardness: 9 on the Mohs scale
Color: Deep royal blue
Luster: Vitreous (glass-like)

Identified July 16, 2026More gemstone →

Explore Blue Sapphire in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 9 on the Mohs scale. Color: Deep royal blue. Luster: Vitreous (glass-like). Crystal Structure: Trigonal. Specific Gravity: 3.95–4.03. Cleavage: None (has parting).

Formation & geological history

Formed in aluminum-rich metamorphic rocks (like marble or schist) and igneous rocks (like syenite). The blue color is caused by trace amounts of iron and titanium within the aluminum oxide crystal lattice.

Uses & applications

Predominantly used in high-end jewelry (rings, bracelets, necklaces). Industrial-grade sapphire (synthetic) is used for watch crystals, electronic wafers, and high-pressure windows due to its extreme hardness.

Geological facts

Sapphire is the birthstone for September and is the second hardest natural substance on Earth after diamond. Historically, sapphires symbolized nobility, truth, and sincerity, famously seen in the engagement ring of Princess Diana.

Field identification & locations

Identification includes checking for 'silk' (rutile inclusions), lack of bubbles (which indicate glass), and color zoning. Major sources include Sri Lanka, Madagascar, Thailand, and Montana (USA). Diamonds or white topaz are often used as accents in jewelry settings.