Blue Sapphire

Physical Properties

Hardness: 9 on the Mohs scale; Color: Deep blue; Luster: Vitreous (glass-like); Crystal structure: Trigonal/Hexagonal; Cleavage: None (has parting); Specific gravity: 3.95–4.03.

Formation & Geological History

Formed in aluminum-rich metamorphic rocks (like marble or schist) or igneous rocks (like syenite) under high pressure and temperature. Commonly found in secondary alluvial deposits (riverbeds).

Uses & Applications

Primary use is in high-end jewelry. Industrial uses (synthetic) include scratch-resistant watch crystals, optical components, and electronic substrates.

Geological Facts

Sapphire is the birthstone for September and the traditional gift for a 45th wedding anniversary. All non-red gem-quality corundums are called sapphires, though blue is the most famous.

Field Identification & Locations

Identify in the field by its extreme hardness (scratches glass and steel easily) and hex-barrel crystal shape. Look for intense blue color in river gravels near volcanic or metamorphic contacts.

Identified on: 4/27/2026

Mode: Standard