mineral
Tumbled agate/chalcedony
Microcrystalline quartz (SiO₂), likely agate or jasper-bearing chalcedony
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; waxy to vitreous luster, translucent cream, gray, tan, and reddish-brown colors, with faint curved banding and no visible cleavage. Specific gravity is approximately 2.6; the rounded shape indicates mechanical tumbling.
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Physical properties
Hardness 6.5–7 Mohs; waxy to vitreous luster, translucent cream, gray, tan, and reddish-brown colors, with faint curved banding and no visible cleavage. Specific gravity is approximately 2.6; the rounded shape indicates mechanical tumbling.
Formation & geological history
Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and quartz. Formation commonly occurred during the Cenozoic or older volcanic episodes, depending on locality.
Uses & applications
Used for ornamental objects, cabochons, beads, paperweights, and lapidary collections; this modest tumbled piece has mainly decorative value.
Geological facts
Agate’s bands develop from changing chemistry, iron content, and fluid conditions during repeated silica deposition. Red-brown coloration commonly reflects iron oxides.
Field identification & locations
Identify by its waxy translucency, quartz hardness, curved or diffuse banding, and resistance to scratching by steel; a glassy conchoidal fracture is diagnostic in rough material. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States.
