mineral

Rough Corundum (likely Sapphire/Zircon-bearing)

Aluminium Oxide (Al2O3)

Hardness: 9 on the Mohs scale. Color: Brownish-yellow to translucent tan. Luster: Adamantine to vitreous. Crystal structure: Hexagonal/Trigonal (often barrel-shaped). Cleavage: None (has rhombohedral parting). Specific Gravity: 3.95–4.10.

Hardness: 9 on the Mohs scale
Color: Brownish-yellow to translucent tan
Luster: Adamantine to vitreous

Identified February 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed in silica-poor igneous rocks (syenites, pegmatites) or metamorphic rocks (marbles, schists). It is often found in alluvial deposits (placer deposits) where it has been weathered out of the parent rock and transported by water.

Uses & applications

Industrial use as an abrasive (emery) due to high hardness. Gem-quality specimens are cut into Sapphires or Rubies for jewelry. Also used in high-pressure scientific instruments and scratch-resistant watch crystals.

Geological facts

Corundum is the second hardest natural mineral after diamond. Common opaque varieties like this specimen are frequently used for mechanical parts and sandpaper, whereas transparent versions are some of the most expensive gemstones in the world.

Field identification & locations

Identify in the field by its extreme hardness (it will scratch glass and quartz easily) and its high density. It often displays a distinct hexagonal cross-section or 'rungs' on the surface of the crystal known as striations.

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