igneous
Weathered volcanic tuff or breccia
Lithified volcanic ash and rock fragments; likely rhyolitic to andesitic tuff/breccia
AI-generated identification · may be incorrectTan to reddish-brown, fine earthy matrix with angular pale fragments and darker clasts; dull to slightly gritty luster. Typically very porous, low density, and soft—about Mohs 3–6 depending on cementation; no obvious cleavage or large crystals.
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Physical properties
Tan to reddish-brown, fine earthy matrix with angular pale fragments and darker clasts; dull to slightly gritty luster. Typically very porous, low density, and soft—about Mohs 3–6 depending on cementation; no obvious cleavage or large crystals.
Formation & geological history
Formed when volcanic ash and fragmented lava were deposited, compacted, and cemented. The specimen is likely Cenozoic volcanic material, consistent with the extensive volcanic terrain around central Arizona, though exact age requires laboratory study.
Uses & applications
Mostly used as a building or landscaping stone and collected as a representative volcanic specimen; porous tuff can also be carved. Little jewelry value.
Geological facts
The irregular layering and contrasting angular fragments suggest tuffaceous breccia rather than a single crystalline lava. Weathering commonly produces the crumbly tan rind visible here.
Field identification & locations
In the field, test whether fresh surfaces are gritty and porous and contain embedded angular rock fragments. Around 33.5°N, 110.8°W, volcanic tuffs, breccias, basalts, and hydrothermal alteration products are plausible; hand-lens and acid testing may help distinguish it from sandstone or cemented fault breccia.
