mineral
Polished agate geode
Chalcedony (microcrystalline quartz, SiO₂) with quartz druse crystals
AI-generated identification · may be incorrectTypically Mohs hardness 6.5–7, vitreous to waxy luster, translucent gray-white banding, and a hollow cavity lined with sparkling quartz crystals; quartz has a trigonal crystal structure and no cleavage. The specimen appears polished and possibly enhanced, with minor iron-oxide brown coloration inside.
Identified More mineral →
Explore Polished agate geode in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically Mohs hardness 6.5–7, vitreous to waxy luster, translucent gray-white banding, and a hollow cavity lined with sparkling quartz crystals; quartz has a trigonal crystal structure and no cleavage. The specimen appears polished and possibly enhanced, with minor iron-oxide brown coloration inside.
Formation & geological history
Agate forms when silica-rich groundwater fills gas cavities in volcanic rock, depositing concentric chalcedony bands and later quartz crystals. Formation commonly occurred in Cenozoic to older basaltic volcanic environments over thousands to millions of years.
Uses & applications
Used as a decorative specimen, paperweight, or jewelry and craft material; thin slices are used for cabochons and ornaments. It has little industrial value in this small polished form.
Geological facts
The outer bands are cryptocrystalline quartz, while the cavity contains larger euhedral quartz crystals. Agate’s vivid banding develops through repeated changes in groundwater chemistry and silica availability.
Field identification & locations
Identify it by concentric bands, waxy translucent chalcedony, a hollow drusy center, and hardness sufficient to scratch glass. Common sources include Brazil, Uruguay, Mexico, India, and the United States.
