gemstone

Sapphire

Corundum (Al2O3)

Hardness: 9 on Mohs scale. Color: Deep blue (likely translucent to opaque). Luster: Vitreous to sub-adamantine. Crystal structure: Hexagonal (Trigonal). Cleavage: None, but shows parting.

Hardness: 9 on Mohs scale
Color: Deep blue (likely translucent to opaque)
Luster: Vitreous to sub-adamantine

Identified July 17, 2026More gemstone →

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Physical properties

Hardness: 9 on Mohs scale. Color: Deep blue (likely translucent to opaque). Luster: Vitreous to sub-adamantine. Crystal structure: Hexagonal (Trigonal). Cleavage: None, but shows parting.

Formation & geological history

Formed in aluminum-rich metamorphic rocks (schists, gneisses) or igneous rocks (syenites). This faceted specimen is a cut gemstone. Montana (near the user's location) is famous for Yogo and Missouri River sapphires.

Uses & applications

Primarily used in high-end jewelry. Industrial-grade sapphire is used for watch crystals, electronics, and scratch-resistant windows.

Geological facts

Sapphire is the second hardest natural mineral after diamond. The blue color is caused by trace amounts of iron and titanium within the aluminum oxide crystal lattice.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel or quartz) and high specific gravity. Faceted specimens like this should be evaluated by a gemologist to distinguish natural from synthetic material.