igneous
Weathered iron-stained quartz-rich rock, possibly rhyolite or quartzite
Indeterminate silica-rich rock; likely quartz (SiO₂) with iron oxides and clay alteration
AI-generated identification · may be incorrectPale cream, tan, orange, and reddish-brown; dull to slightly waxy luster; granular and heavily weathered, with porous cavities and dark iron-oxide staining. Quartz hardness is 7 Mohs, but the overall specimen may be softer from alteration; cleavage is absent or poor, and specific gravity is approximately 2.5–2.7.
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Physical properties
Pale cream, tan, orange, and reddish-brown; dull to slightly waxy luster; granular and heavily weathered, with porous cavities and dark iron-oxide staining. Quartz hardness is 7 Mohs, but the overall specimen may be softer from alteration; cleavage is absent or poor, and specific gravity is approximately 2.5–2.7.
Formation & geological history
Likely formed from silica-rich volcanic rock or metamorphosed sandstone, then altered and oxidized near the surface; the geological age cannot be determined from the photograph. The cavities may reflect weathering of dissolved minerals or former gas voids.
Uses & applications
Primarily a field or display specimen; not suitable for construction without confirmed composition. It may have modest lapidary interest if sound interior material is present.
Geological facts
The yellow-red coloration typically comes from limonite, goethite, or hematite. The rough, friable surface indicates substantial chemical weathering.
Field identification & locations
Common in weathered outcrops, gravel deposits, and iron-rich soils worldwide; test a fresh edge for abundant glassy quartz, use a steel file for hardness, and check for fizzing with dilute acid. A precise identification requires a fresh fracture, locality, streak, and possibly thin-section or XRF analysis.
