mineral

Rough Dark Green Sapphire

Corundum (Al2O3)

Hardness: 9 on the Mohs scale. Color: Dark deep green to nearly black (melanic). Luster: Adamantine to vitreous. Crystal structure: Hexagonal/Trigonal. Cleavage: None (has parting). Specific Gravity: 3.95–4.10.

Hardness: 9 on the Mohs scale
Color: Dark deep green to nearly black (melanic)
Luster: Adamantine to vitreous

Identified February 18, 2026More mineral →

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Physical properties

Formation & geological history

Formed in aluminum-rich metamorphic rocks (schist/gneiss) or igneous rocks (alkali basalts/syenites). Most specimens are found in alluvial deposits (rivers/streams) where they have been weathered out of their host rock and water-worn over millions of years.

Uses & applications

Used primarily in jewelry as a gemstone when high clarity is present. Non-gem grade Corundum is used industrially as an abrasive (emery) for grinding and polishing due to its extreme hardness.

Geological facts

Green sapphires were once called 'Oriental Emeralds' despite being a completely different mineral species (Corundum vs. Beryl). They get their green color from trace amounts of iron within the crystal lattice.

Field identification & locations

Identify in the field by its weight (feels heavy for its size) and extreme hardness; it will scratch glass and almost all other minerals except diamond. Commonly found in gem gravels in Australia, Thailand, and Montana, USA.