mineral

Tumbled brown agate (probable)

Microcrystalline quartz, SiO₂ (chalcedony/agate)

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, waxy to vitreous luster, brown to black banding or inclusions, and no visible cleavage; polished surfaces are rounded and glossy. The dark markings could also reflect iron/manganese-rich dendrites or another included mineral.

Identified September 4, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and quartz in successive layers over millions of years. Common source rocks are ancient basaltic lavas and volcanic geodes.

Uses & applications

Used for cabochons, beads, carvings, bookends, and lapidary collections; its toughness makes it suitable for polished decorative objects.

Geological facts

Agate is a variety of chalcedony rather than a separate mineral species, and its banding records changing chemistry during cavity filling.

Field identification & locations

Identify by its glassy/waxy polish, hardness, translucency at thin edges, and cryptocrystalline banding; common localities include Brazil, Uruguay, India, Mexico, and the United States. A definitive identification would require observing the interior or testing hardness and specific gravity.