mineral
Brown agate (chalcedony)
Microcrystalline quartz, SiO₂; likely iron-stained chalcedony
AI-generated identification · may be incorrectRough, mottled brown-gray specimen with a waxy to dull luster; quartz hardness is 6.5–7, with no cleavage and conchoidal fracture. The photo does not show enough detail to confirm banding or translucency.
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Physical properties
Rough, mottled brown-gray specimen with a waxy to dull luster; quartz hardness is 6.5–7, with no cleavage and conchoidal fracture. The photo does not show enough detail to confirm banding or translucency.
Formation & geological history
Forms as silica-rich fluids fill cavities and fractures, depositing cryptocrystalline quartz; iron impurities can produce brown colors. Agate occurs in rocks of many ages, commonly in volcanic cavities.
Uses & applications
Agate is used for beads, cabochons, ornaments, and small decorative objects; rough pieces are also collected.
Geological facts
Agate is a variety of chalcedony, not a separate mineral species; its identifying bands may be subtle or absent in some material.
Field identification & locations
Look for waxy luster, curved fracture surfaces, and possible translucent edges or bands; common sources include Brazil, Uruguay, India, and the western United States. A photo alone cannot reliably distinguish agate from other brown chalcedony or silica-rich rocks.
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