igneous
Reddish-brown granitic pebble
Granite, likely biotite granite or granodiorite
AI-generated identification · may be incorrectCoarse-grained, speckled gray, pink, black, and rusty-brown appearance; interlocking quartz and feldspar with dark biotite or hornblende. Hardness about 6–7 Mohs, nonmetallic vitreous-to-dull luster, massive texture, no cleavage as a whole, and specific gravity around 2.6–2.8.
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Physical properties
Coarse-grained, speckled gray, pink, black, and rusty-brown appearance; interlocking quartz and feldspar with dark biotite or hornblende. Hardness about 6–7 Mohs, nonmetallic vitreous-to-dull luster, massive texture, no cleavage as a whole, and specific gravity around 2.6–2.8.
Formation & geological history
Formed when silica-rich magma slowly crystallized deep in the continental crust, commonly during Precambrian to Phanerozoic mountain-building events; the pebble was later weathered and transported.
Uses & applications
Used extensively as building stone, countertops, monuments, aggregate, and landscaping rock; small attractive pieces have modest collecting value.
Geological facts
The rusty color usually reflects oxidation of iron-bearing biotite or hornblende. Granite’s visible crystals indicate slow underground cooling rather than volcanic eruption.
Field identification & locations
Identify it by visible quartz, pale feldspar, and scattered black mica/amphibole grains, with no layering or foliation. Common in continental mountain belts, glacial deposits, stream beds, and crushed-stone surfaces.
