mineral
Botryoidal chalcedony (possibly common opal)
Microcrystalline quartz, SiO₂; pale portions may include hydrated silica opal, SiO₂·nH₂O
AI-generated identification · may be incorrectWhite to translucent, rounded botryoidal surfaces with a waxy to vitreous luster; quartz hardness about 6.5–7 Mohs, opal about 5.5–6.5. No visible cleavage; cryptocrystalline or amorphous structure and typically low-to-moderate specific gravity (about 2.0–2.65).
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Physical properties
White to translucent, rounded botryoidal surfaces with a waxy to vitreous luster; quartz hardness about 6.5–7 Mohs, opal about 5.5–6.5. No visible cleavage; cryptocrystalline or amorphous structure and typically low-to-moderate specific gravity (about 2.0–2.65).
Formation & geological history
Forms when silica-rich groundwater deposits successive layers in cavities, fractures, or vesicles, commonly in volcanic rocks; specimens may range from ancient to recent depending on the host deposit.
Uses & applications
Used as a lapidary stone, cabochon, carving material, and collectible specimen; translucent colorful varieties may be sold as gemstone material.
Geological facts
The bubble-like texture is called botryoidal, meaning grape-shaped. Its appearance can resemble white chalcedony, common opal, or chalcedony coating a porous host.
Field identification & locations
Look for hardness above glass, conchoidal fracture, waxy luster, and lack of fizz in dilute acid; a loupe may reveal translucent chalcedony layers. Common sources include volcanic regions in the western United States, Mexico, Brazil, Turkey, and Australia.
