mineral
Polished banded agate
Microcrystalline quartz (SiO₂), chiefly chalcedony
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent gray, cream, and honey-brown bands with a waxy to vitreous luster. Trigonal quartz in microscopic fibers; no distinct cleavage, conchoidal fracture. The piece appears cut and polished.
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Physical properties
Hardness 6.5–7 Mohs; translucent gray, cream, and honey-brown bands with a waxy to vitreous luster. Trigonal quartz in microscopic fibers; no distinct cleavage, conchoidal fracture. The piece appears cut and polished.
Formation & geological history
Silica-rich groundwater deposited successive layers in a cavity, later forming banded chalcedony; agates occur in volcanic rocks and sedimentary settings across many geological ages.
Uses & applications
Used for jewelry, ornaments, carvings, and lapidary collections; agate has also been used for small tools and decorative objects.
Geological facts
Agate banding records changes in silica deposition and trace impurities; some bands form concentric patterns around a cavity.
Field identification & locations
Identify by its curved, contrasting bands, translucency, and glassy/waxy polish; common sources include Brazil, Uruguay, India, and the western United States. Similar-looking banded materials may require magnification or testing to distinguish.
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