mineral
Tumbled banded agate
Agate, a microcrystalline variety of quartz (SiO₂)
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; gray, cream, and brown banding with a waxy to vitreous luster and no visible cleavage. Its microcrystalline quartz has a trigonal crystal structure; the rounded surface appears naturally banded and tumbled smooth.
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Physical properties
Hardness 6.5–7 Mohs; gray, cream, and brown banding with a waxy to vitreous luster and no visible cleavage. Its microcrystalline quartz has a trigonal crystal structure; the rounded surface appears naturally banded and tumbled smooth.
Formation & geological history
Agate forms as silica-rich fluids fill cavities in volcanic rocks, depositing successive bands; the exact age depends on the host rock. Common sources include Brazil, Uruguay, India, and the United States.
Uses & applications
Used for jewelry, beads, carvings, and decorative objects; agate is also collected as a polished specimen.
Geological facts
The fine bands record changes in silica deposition and fluid conditions as the cavity gradually filled.
Field identification & locations
Look for curved or concentric color bands and a hardness sufficient to scratch glass; the pictured stone is polished, so fresh fracture and natural texture are not visible.
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