mineral

Blue Sapphire

Corundum (Al2O3 with trace Titanium and Iron)

Hardness: 9.0 on the Mohs scale. Color: Deep royal blue. Luster: Vitreous (glass-like). Crystal structure: Trigonal/Hexagonal. Cleavage: None (has conchoidal fracture). Specific Gravity: 3.98 - 4.06.

Hardness: 9
Color: Deep royal blue
Luster: Vitreous (glass-like)

Identified March 11, 2026More mineral →

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Physical properties

Hardness: 9.0 on the Mohs scale. Color: Deep royal blue. Luster: Vitreous (glass-like). Crystal structure: Trigonal/Hexagonal. Cleavage: None (has conchoidal fracture). Specific Gravity: 3.98 - 4.06.

Formation & geological history

Formed deep within the Earth's crust under high pressure and temperature in metamorphic rocks like marble or schist, or in igneous rocks like basalt. Many specimens are found in secondary alluvial deposits (riverbeds).

Uses & applications

Primarily used as a precious gemstone in jewelry. Industrial-grade sapphire (synthetic) is used for watch crystals, high-durability windows, and abrasive tools due to its extreme hardness.

Geological facts

Sapphire is the second hardest natural substance on Earth after diamond. While usually blue, corundum comes in every color of the rainbow; any color of corundum that isn't red is technically a sapphire (red is strictly called Ruby).

Field identification & locations

Identify in the field by its high density (feels heavy for its size), hexagonal barrel shape in raw form, and inability to be scratched by steel or quartz. Common locations include Sri Lanka, Madagascar, Myanmar, and Montana, USA.

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