mineral

Rough Sapphire (Corundum)

Corundum (Al2O3)

Hardness: 9 on Mohs scale. Color: Deep blue, greenish-blue, or brownish in rough form. Luster: Adamantine to vitreous. Crystal structure: Trigonal/Hexagonal. Cleavage: None (has parting). Specific gravity: 3.95–4.10.

Hardness: 9 on Mohs scale
Color: Deep blue, greenish-blue, or brownish in rough form
Luster: Adamantine to vitreous

Identified February 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed in aluminum-rich igneous and metamorphic rocks (such as schist and gneiss) or concentrated in alluvial deposits (placer deposits) through weathering and erosion of primary source rock.

Uses & applications

High-quality specimens are faceted for jewelry. Industrial grade corundum is used as an abrasive (emery), in sandpaper, and for scratch-resistant 'sapphire glass' in watches and electronics.

Geological facts

Sapphire is the second hardest natural mineral known to man. It is chemically identical to Ruby, though Rubies are distinguished by their red color caused by chromium, while blue sapphires are colored by iron and titanium.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by quartz or steel) and its weight, which is significantly higher than most rocks of its size. Commonly found in Sri Lanka, Madagascar, Australia, and Montana (USA).