mineral
Polished black-and-brown agate pebble
Microcrystalline quartz (SiO₂), likely chalcedony/agate
AI-generated identification · may be incorrectMohs hardness 6.5–7; translucent brown areas with dark bands or patches and a glossy polish. Quartz has a trigonal crystal structure; the microcrystalline aggregate has no visible cleavage and conchoidal fracture.
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Physical properties
Mohs hardness 6.5–7; translucent brown areas with dark bands or patches and a glossy polish. Quartz has a trigonal crystal structure; the microcrystalline aggregate has no visible cleavage and conchoidal fracture.
Formation & geological history
Silica-rich fluids deposited chalcedony in cavities or fractures, commonly in volcanic rocks. The image cannot establish its geological age or exact source.
Uses & applications
Used for jewelry, ornaments, and lapidary collecting; this small tumbled specimen has modest value.
Geological facts
Agate is a variety of chalcedony, and its colors and patterns can be natural or enhanced by treatment.
Field identification & locations
The smooth, rounded shape indicates tumbling or water wear; waxy-to-glassy luster and hardness help distinguish it from softer lookalikes. Agates occur worldwide, including Brazil, Uruguay, India, and the western United States.
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