mineral
Tumbled banded agate
Agate, a variety of chalcedony (microcrystalline SiO₂)
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; glossy vitreous-to-waxy luster, rounded polished surface, and brown, cream, and gray bands. Quartz crystals are microscopic and typically arranged in fibrous layers; specific gravity is about 2.6.
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Physical properties
Hardness 6.5–7 Mohs; glossy vitreous-to-waxy luster, rounded polished surface, and brown, cream, and gray bands. Quartz crystals are microscopic and typically arranged in fibrous layers; specific gravity is about 2.6.
Formation & geological history
Silica-rich groundwater deposits chalcedony in cavities and fractures, often in volcanic rocks; agate forms over geological time, with ages varying by deposit.
Uses & applications
Used for jewelry, ornaments, and lapidary collecting; agate is also used for small decorative and technical objects.
Geological facts
Agate’s characteristic bands record successive silica deposition, and some banding becomes visible only when cut or polished.
Field identification & locations
Identify by its waxy polish, hardness, and curved or irregular bands; common sources include Brazil, Uruguay, India, and the United States. Typical tumbled specimens sell for about $2–$15, depending on size and pattern.
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