mineral
Banded agate (likely Montana/Columbia River-style agate)
Microcrystalline quartz, SiO₂ (chalcedony with mogánite; iron-oxide staining)
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; white, cream, tan, and brown concentric banding; waxy to dull luster; cryptocrystalline, with no visible cleavage and conchoidal fracture. The specimen appears naturally fractured or roughly cut, not glass or ceramic.
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Physical properties
Hardness 6.5–7 Mohs; white, cream, tan, and brown concentric banding; waxy to dull luster; cryptocrystalline, with no visible cleavage and conchoidal fracture. The specimen appears naturally fractured or roughly cut, not glass or ceramic.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and quartz. Individual bands may form over thousands to millions of years, commonly in Cenozoic basalt provinces; the regional occurrence near northeastern Washington is geologically plausible.
Uses & applications
Used for cabochons, slabs, carvings, ornaments, and lapidary collecting; less commonly as aggregate or decorative stone.
Geological facts
The curved “fortification” bands record changing chemistry and flow conditions during cavity filling. Dark lines are likely manganese or iron-bearing inclusions and fractures rather than true black minerals.
Field identification & locations
Identify by translucent edges, waxy feel, very hard silica, curved rhythmic bands, and inability to scratch it with a steel knife (though quartz can scratch glass). Common in Washington and neighboring Columbia Plateau volcanic terrains, often as agate nodules or seams.
