metamorphic
Quartzite with Chalcedony
Metamorphosed Quartz-rich Sandstone (SiO2)
Hardness: 7 (Mohs scale), Color: Creamy white with orange/yellow iron staining, Luster: Waxy to vitreous when wet, Crystal structure: Microcrystalline/Massive, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Creamy white with orange/yellow iron staining, Luster: Waxy to vitreous when wet, Crystal structure: Microcrystalline/Massive, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure. The specimen shows significant rounding from river transport, likely dating from the Pleistocene epoch within regional alluvial deposits.
Uses & applications
Commonly used as a construction aggregate, in landscaping, and sometimes as a minor gemstone (agate/chalcedony variety) for lapidary tumbling.
Geological facts
This specimen displays 'iron staining' where iron oxides have leached into the micro-fissures of the quartz, creating the yellow-orange patch. It is a very durable stone that survives long-distance transport in river systems.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its grainy but fused texture. In the Portland/Willamette Valley area (45.5°N, 122.8°W), these are ubiquitous in the Columbia River Basalt Group's associated gravels.
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