mineral

Blue Sapphire

Corundum (Al2O3)

Hardness: 9 on the Mohs scale. Color: Deep midnight blue to cornflower blue. Luster: Adamantine to vitreous. Crystal structure: Trigonal (hexagonal scalenohedral). Cleavage: None (has parting). Specific gravity: 3.95–4.03.

Hardness: 9 on the Mohs scale
Color: Deep midnight blue to cornflower blue
Luster: Adamantine to vitreous

Identified March 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed in aluminum-rich metamorphic rocks (like marble or schist) or igneous rocks (like pegmatites) under high heat and pressure. Most gem-quality specimens are found in secondary alluvial deposits (riverbeds) where they have weathered out of their host rock.

Uses & applications

Primarily used in high-end jewelry (faceted gemstones) and as a birthstone for September. Industrial-grade sapphire (usually synthetic) is used for scratch-resistant watch crystals, optical components, and abrasives.

Geological facts

Sapphire is the second hardest natural substance on Earth after diamond. While the term 'sapphire' usually refers to the blue variety of Corundum, it can come in every color of the rainbow except red (which is classified as Ruby).

Field identification & locations

In the field, it is identified by its extreme hardness (cannot be scratched by quartz or steel) and high density. Commonly found in locations like Sri Lanka, Myanmar (Burma), Madagascar, and Australia. Collectors look for clarity, 'silk' (fine rutile inclusions), and color saturation.