igneous
Granite Cobble / Granitoid Pebble
Granitoid (Plutonic felsic/intermediate rock)
AI-generated identification · may be incorrectHardness 6-7 on Mohs scale; color is mottled gray, off-white, and dark gray/black; dull to sub-vitreous luster on crystalline faces; phaneritic (coarse-grained) crystalline texture; specific gravity ~2.6-2.75.
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Physical properties
Hardness 6-7 on Mohs scale; color is mottled gray, off-white, and dark gray/black; dull to sub-vitreous luster on crystalline faces; phaneritic (coarse-grained) crystalline texture; specific gravity ~2.6-2.75.
Formation & geological history
Formed deep underground by the slow crystallization of felsic to intermediate magma. Subsequent tectonic uplift and surface weathering exposed the rock, followed by river or glacial transport that mechanically smoothed it into a rounded cobble.
Uses & applications
Commonly used in landscaping, road construction aggregate, ballast, architectural facings, and polished decorative stone.
Geological facts
Granite forms a major part of the Earth's continental crust. Its durability and resistance to chemical weathering allow large cobbles like this to survive long transport distances in rivers and glacial flows.
Field identification & locations
Identifiable by its interlocked quartz, feldspar, and occasional mica/amphibole crystals without pronounced metamorphic banding. Ubiquitous in riverbeds, glacial drift zones, and coastal pebble beaches worldwide.
