igneous
Weathered granite or granitic gneiss pebble
Quartz–feldspar–mica granitoid; possibly weakly gneissic
AI-generated identification · may be incorrectHardness about 6–7 Mohs; tan-brown from weathering, with dull earthy luster and visible granular quartz/feldspar/mica. Interlocking crystals, no obvious cleavage as a whole rock, and moderate-to-high specific gravity (~2.6–2.8).
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Physical properties
Hardness about 6–7 Mohs; tan-brown from weathering, with dull earthy luster and visible granular quartz/feldspar/mica. Interlocking crystals, no obvious cleavage as a whole rock, and moderate-to-high specific gravity (~2.6–2.8).
Formation & geological history
Formed by slow cooling of silica-rich magma deep in Earth, likely Precambrian to Paleozoic in age, then exposed and rounded by weathering and transport. The brown coating reflects iron-oxide alteration.
Uses & applications
Commonly used as aggregate, road stone, building stone, and landscaping material; this weathered specimen has little jewelry value.
Geological facts
The pale, blocky grains are likely feldspar, gray translucent grains quartz, and dark flecks biotite or amphibole. Surface rounding indicates abrasion in a stream, beach, or glacial environment.
Field identification & locations
Identify by its coarse interlocking texture, abundant light minerals, and lack of layering or vesicles; a streak test is usually white, and it will not fizz with dilute hydrochloric acid unless carbonate contamination is present. Common worldwide in continental crust and gravel deposits.
