mineral

Blue Sapphire

Corundum (Al2O3 with iron and titanium trace elements)

Hardness: 9 on the Mohs scale; Color: Deep blue; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (basal parting); Specific Gravity: 3.98 - 4.06

Hardness: 9 on the Mohs scale
Color: Deep blue
Luster: Vitreous to sub-adamantine

Identified June 23, 2026More mineral →

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Physical properties

Hardness: 9 on the Mohs scale; Color: Deep blue; Luster: Vitreous to sub-adamantine; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (basal parting); Specific Gravity: 3.98 - 4.06

Formation & geological history

Formed in aluminum-rich metamorphic rocks (schists and gneisses) and certain igneous rocks like syenites. They are often found in secondary alluvial deposits where they have weathered out of the host rock.

Uses & applications

Primary use is in high-end jewelry as a gemstone. Industrial applications include scratch-resistant windows, watch crystals, and high-quality electronic components due to its extreme hardness and durability.

Geological facts

Sapphire is the second hardest natural substance on Earth after diamond. While the term sapphire usually refers to the blue variety, corundum comes in every color except red (which is classified as ruby). The blue color is specifically caused by trace amounts of iron and titanium.

Field identification & locations

Identify by its high refractive index, extreme hardness, and lack of cleavage. In the field, look for rounded or water-worn hexagonal barrels in riverbeds or alluvial gravels. Common locations include Sri Lanka, Madagascar, Australia, and Thailand.

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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