gemstone

Ruby cabochons

Corundum, aluminum oxide (Al₂O₃), colored red by chiefly chromium

AI-generated identification · may be incorrect

Mohs hardness 9; vivid red to purplish-red color, vitreous luster, trigonal crystal structure, and no true cleavage. These appear to be polished oval cabochons, likely translucent to opaque, with some inclusions and surface irregularities.

Identified September 10, 2026More gemstone →

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Physical properties

Formation & geological history

Ruby forms mainly in metamorphic rocks such as marble and aluminous gneiss, and occasionally in basalt-related deposits. Most gem rubies are geologically ancient, commonly formed during Precambrian to Mesozoic metamorphic events.

Uses & applications

Used in jewelry, ornament, watchmaking, and precision bearings; synthetic ruby is also important for lasers and industrial components. Commercial value depends strongly on color, transparency, treatment, size, and origin.

Geological facts

Fine untreated “pigeon-blood” ruby is among the world’s most valuable gemstones. Natural rubies commonly show rutile inclusions (“silk”); many commercial stones are heat-treated or fracture-filled.

Field identification & locations

Identify by exceptional hardness, red color, strong luster, and lack of cleavage; verify with refractive-index testing and microscopy because red glass, garnet, spinel, and dyed corundum can look similar. Major sources include Myanmar, Mozambique, Sri Lanka, Thailand, Vietnam, and Madagascar.