igneous
Rounded quartz-rich river cobble (probable rhyolite/granite-derived stone)
Indeterminate felsic igneous cobble; likely quartz–feldspar aggregate with minor iron oxides
AI-generated identification · may be incorrectPale gray-beige, fine-grained and weakly speckled, dull to slightly earthy luster, no obvious cleavage or crystal faces; estimated Mohs hardness 6–7, with moderate-high density. Surface is smoothly rounded and weathered, consistent with water transport.
Identified More igneous →
Explore Rounded quartz-rich river cobble (probable rhyolite/granite-derived stone) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Pale gray-beige, fine-grained and weakly speckled, dull to slightly earthy luster, no obvious cleavage or crystal faces; estimated Mohs hardness 6–7, with moderate-high density. Surface is smoothly rounded and weathered, consistent with water transport.
Formation & geological history
Probably eroded from felsic volcanic or intrusive rocks and rounded in an arroyo or river. Exact age cannot be determined photographically; the Las Cruces region exposes nearby volcanic, sedimentary, and alluvial materials of Cenozoic to Quaternary age.
Uses & applications
Typically a landscaping or decorative cobble; not gem-quality. If sufficiently hard and uniform, it may be used as a polishing stone or aggregate.
Geological facts
The small rusty-orange spot is likely iron-oxide staining. The image does not show diagnostic texture for a precise mineral or rock identification.
Field identification & locations
Common regional alternatives include rhyolite, granite-derived alluvial cobbles, and silicified volcanic rock. Test a fresh edge: quartz-rich material should scratch glass; dilute acid should produce little or no fizz, unlike limestone. A hand lens or cut face would improve identification.
