mineral

Corundum (Sapphire/Ruby in Matrix)

Corundum (Al2O3)

Hardness: 9 on Mohs scale. Color: Greenish-blue to brownish in its raw state. Luster: Adamantine to vitreous. Crystal structure: Hexagonal/Trigonal. Cleavage: None (has parting). Specific gravity: 3.9–4.1.

Hardness: 9 on Mohs scale
Color: Greenish-blue to brownish in its raw state
Luster: Adamantine to vitreous

Identified April 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed in silica-poor igneous rocks or through regional metamorphism of shale and limestone. This specimen appears to be an alluvial or rough crystal found in metamorphic environments or river beds.

Uses & applications

Used as an abrasive in industry due to its extreme hardness. High-quality transparent pieces are used as gemstones (Sapphires and Rubies). Common rough pieces are kept by mineral collectors.

Geological facts

Corundum is the second hardest natural mineral known to man, after diamond. The blue color is typically caused by traces of iron and titanium, while red (Ruby) is caused by chromium.

Field identification & locations

Identify in the field by its high density (feels heavy for its size) and its ability to scratch almost any other mineral except diamond. Look for hexagonal barrel-shaped crystal habits.

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