mineral

Botryoidal chalcedony/geode fragment

Chalcedony (microcrystalline quartz, SiO₂), with possible drusy quartz and iron-oxide staining

AI-generated identification · may be incorrect

Tan-brown, gray, and cream banding surrounds a cavity lined with tiny sparkling quartz crystals; vitreous to waxy luster, hardness about 6.5–7 Mohs, conchoidal fracture, no cleavage, and specific gravity near 2.6. The rounded bubbly texture is botryoidal, though exact identification is limited by the photograph.

Identified August 13, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited successive layers in a cavity or fracture, later coating the interior with drusy quartz; brown coloration commonly comes from iron oxides. Such material forms in volcanic rocks and sedimentary replacement zones, generally at shallow geological temperatures over extended periods.

Uses & applications

Commonly cut and polished for cabochons, display pieces, bookends, and lapidary specimens; attractive drusy surfaces may be used in jewelry. Ordinary pieces have modest commercial value.

Geological facts

Chalcedony is quartz composed of extremely fine intergrowths of quartz varieties. Color and banding can resemble agate, jasper, or silicified limestone, so hardness and acid testing help distinguish it.

Field identification & locations

Look for waxy chalcedony, curved banding, cavity linings, and resistance to scratching by steel; it should not fizz with dilute hydrochloric acid unless carbonate is present. Common sources include Brazil, Uruguay, Mexico, India, and the western United States.