mineral

Polished dark agate or jasper pebble

Microcrystalline quartz (SiO₂), likely chalcedony with iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; dark brown to black, with a polished vitreous-to-waxy luster and subtle lighter veining. Quartz is trigonal microscopically, lacks visible cleavage, and has a typical specific gravity near 2.6.

Identified September 3, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich fluids fill cavities or fractures in volcanic rock, with iron oxides producing the brown-black coloration; commonly Cenozoic to older, depending on its host rock. The shape shown is likely tumbled or naturally water-worn and polished.

Uses & applications

Used for cabochons, beads, carvings, paperweights, and inexpensive collector specimens; durable enough for decorative objects but not typically a high-value gemstone.

Geological facts

Agate and jasper are varieties of chalcedony distinguished by texture and opacity: translucent banding favors agate, while opaque material is usually called jasper. The specimen may also be an iron-rich chert if it lacks clear banding.

Field identification & locations

Identify by its glassy/waxy surface, lack of obvious cleavage, high hardness, and inability to scratch it with a steel knife; quartz should scratch ordinary glass. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.