gemstone

Blue opal cabochon (likely common opal)

Opal, hydrated amorphous silica (SiO₂·nH₂O)

AI-generated identification · may be incorrect

Polished, translucent blue cabochon with cloudy inclusions and vitreous-to-waxy luster; hardness about 5.5–6.5 Mohs, no cleavage, and specific gravity about 1.98–2.25. Its amorphous structure distinguishes it from crystalline quartz.

Identified September 18, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater deposits hydrated silica in cavities and fractures, commonly in volcanic rocks or sedimentary formations. Opal deposits range from Cenozoic to older, but the specimen’s locality and age cannot be determined visually.

Uses & applications

Used for cabochon jewelry, ornamental objects, and mineral collecting; blue common opal is generally less valuable than gem opal showing play-of-color.

Geological facts

The blue color may result from microscopic inclusions or finely distributed minerals; lack of visible rainbow flashes suggests common opal rather than precious opal.

Field identification & locations

Identify by its low hardness, lightweight feel, waxy luster, conchoidal fracture, and absence of cleavage; avoid prolonged heat or drying, which can cause cracking. Common sources include Peru, Mexico, Australia, Ethiopia, and the United States.