mineral
Tumbled brown agate
Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide inclusions
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent cream, honey-brown, and reddish-brown coloration; waxy to vitreous luster; cryptocrystalline quartz with no cleavage and conchoidal fracture. The smooth, glossy surface indicates tumbling or polishing.
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Physical properties
Hardness 6.5–7 Mohs; translucent cream, honey-brown, and reddish-brown coloration; waxy to vitreous luster; cryptocrystalline quartz with no cleavage and conchoidal fracture. The smooth, glossy surface indicates tumbling or polishing.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony and quartz in layers; iron oxides create the brown-red colors. Individual agate formation may span thousands to millions of years, commonly in Cenozoic or older volcanic terrain.
Uses & applications
Used for cabochons, beads, carvings, paperweights, and decorative objects; durable agate is also used for small industrial bearings and laboratory mortars.
Geological facts
Agate is a variety of banded or patterned chalcedony, though this specimen shows subtle rather than strong banding. Brown coloration commonly reflects hematite or goethite.
Field identification & locations
Identify by its hardness, translucency, waxy appearance, conchoidal fracture, and inability to scratch with a steel knife; it should scratch glass. Common sources include Brazil, Uruguay, India, Mexico, and the United States.
