mineral

Blue Sapphire Crystal (Rough)

Corundum (Aluminum Oxide, Al2O3)

Hardness: 9 on Mohs scale; Color: Grayish-blue to deep blue with a tan/brown host rock or weathered crust; Luster: Adamantine to vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: No true cleavage but show prominent parting.

Hardness: 9 on Mohs scale
Luster: Adamantine to vitreous

Identified June 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed under high-pressure, high-temperature conditions in regional metamorphism or from igneous melts (pegmatites). Often found in alluvial deposits or as primary crystals within schist, gneiss, or marble.

Uses & applications

When gem-quality, it is used for high-end jewelry. Industrial-grade corundum is used for abrasives, watch crystals, and specialized optical windows due to its extreme hardness.

Geological facts

Sapphire is the second hardest natural mineral after diamond. The color comes from trace elements of iron and titanium. Rough hexagonal prisms like this one often show 'silk' (rutile inclusions).

Field identification & locations

Identify by its 6-sided hexagonal barrel shape, extreme hardness (will scratch almost anything but diamond), and high density. Commonly found in Madagascar, Sri Lanka, and Montana, USA.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral