igneous
Weathered quartz-rich rock, possibly granite or quartzite
Indeterminate quartz–feldspar aggregate; likely weathered granite (quartz, feldspar, minor iron oxides)
AI-generated identification · may be incorrectCoarse, irregular granular texture with translucent gray-white quartz and rusty brown iron-oxide staining; vitreous quartz luster, no obvious cleavage in quartz. Quartz hardness is 7 Mohs; overall hardness varies with feldspar and weathering, and specific gravity is approximately 2.6–2.7.
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Physical properties
Coarse, irregular granular texture with translucent gray-white quartz and rusty brown iron-oxide staining; vitreous quartz luster, no obvious cleavage in quartz. Quartz hardness is 7 Mohs; overall hardness varies with feldspar and weathering, and specific gravity is approximately 2.6–2.7.
Formation & geological history
If granite, it crystallized slowly from silica-rich magma deep underground, commonly during Precambrian to Phanerozoic tectonic activity, then weathered at the surface. The rusty coloration reflects oxidation of iron-bearing minerals.
Uses & applications
Common granite is used as crushed stone, aggregate, building stone, and countertops; attractive pieces may be collected but are generally not gem-grade.
Geological facts
Quartz-rich igneous rocks can resemble quartzite or hydrothermal quartz veins in photographs. Iron staining commonly forms limonite/goethite coatings along fractures and weathered surfaces.
Field identification & locations
Likely identification: quartz-rich granite or pegmatitic material. Look for interlocking quartz and feldspar grains, feldspar cleavage, and a scratch test; precise classification requires a fresh surface or thin section. Common worldwide, especially continental shield regions.
