igneous
Red granite or granitic gneiss pebble
Felsic granitoid, likely quartz–feldspar–biotite granite; possible weakly gneissic texture
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled pink-red, gray, black, and cream colors; granular texture with glassy quartz and feldspar, dark biotite/amphibole, and dull weathered surfaces. No obvious cleavage as a rock; feldspar crystals may show cleavage. Specific gravity roughly 2.6–2.8.
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Physical properties
Hardness about 6–7 Mohs; mottled pink-red, gray, black, and cream colors; granular texture with glassy quartz and feldspar, dark biotite/amphibole, and dull weathered surfaces. No obvious cleavage as a rock; feldspar crystals may show cleavage. Specific gravity roughly 2.6–2.8.
Formation & geological history
Crystallized slowly from silica-rich magma deep in the continental crust, probably during Precambrian or younger continental plutonism; later uplift and erosion produced the rounded pebble. The dark streaks may reflect biotite-rich bands or alteration.
Uses & applications
Used widely as crushed stone, aggregate, building stone, countertops, monuments, and landscaping rock; this small specimen has modest collecting value.
Geological facts
The pink-red color commonly comes from potassium feldspar, while black minerals are typically biotite or hornblende. The image could also represent weathered granitic gneiss or a metamorphosed granitoid, which cannot be distinguished confidently without a fresh surface or thin section.
Field identification & locations
Identify by its coarse interlocking crystals, quartz sheen, pink feldspar, and dark mica; it is nonvesicular and much harder than sandstone. Common worldwide, especially in continental shield and mountain regions.
