mineral

Ruby (Corundum)

Corundum (Aluminum Oxide) with chromium trace elements, Al2O3

Hardness: 9 on the Mohs scale. Color: Pink to deep blood-red. Luster: Adamantine to vitreous. Crystal structure: Hexagonal/trigonal. Cleavage: None, but exhibits parting. Specific gravity: 3.97–4.05.

Hardness: 9 on the Mohs scale
Color: Pink to deep blood-red
Luster: Adamantine to vitreous

Identified March 1, 2026More mineral →

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Physical properties

Formation & geological history

Formed through high-grade regional or contact metamorphism of aluminum-rich rocks or in igneous environments such as syenites. They are often found in metamorphic marbles or as alluvial deposits in riverbeds.

Uses & applications

Used primarily as a gemstone for jewelry. Industrial-grade corundum (synthetic or low-quality) is used as an abrasive, in sandpaper, and for creating laser components and watch bearings due to its extreme hardness.

Geological facts

Ruby is the traditional birthstone for July. The presence of chromium is what gives ruby its red color; if the color is anything other than red or pinkish-red, the corundum is classified as a sapphire.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by steel or quartz) and its high density. Found in locations like Myanmar, Sri Lanka, Thailand, and Madagascar. Collectors look for hexagonal crystal habits and a distinct 'glow' under UV light due to fluorescence.

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