igneous
Granite Cobble (or Gneissic Granite)
Granite / Granitic Gneiss
AI-generated identification · may be incorrectHardness 6-7 on Mohs scale; mottled grayish-white, greenish-gray, and black coloration; dull to vitreous luster; phaneritic to weakly foliated texture composed of interlocking quartz, feldspar, and ferromagnesian minerals; specific gravity 2.6-2.7.
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Physical properties
Hardness 6-7 on Mohs scale; mottled grayish-white, greenish-gray, and black coloration; dull to vitreous luster; phaneritic to weakly foliated texture composed of interlocking quartz, feldspar, and ferromagnesian minerals; specific gravity 2.6-2.7.
Formation & geological history
Formed through the slow crystallization of felsic magma beneath the Earth's surface (plutonic), followed by uplift, weathering, and mechanical smoothing into a rounded cobble via fluvial or coastal transport.
Uses & applications
Commonly crushed for construction aggregate, road base, and railroad ballast; higher-grade blocks are cut for dimension stone, countertops, and landscaping.
Geological facts
Granite makes up a major portion of the Earth's continental crust. Its durability and resistance to weathering allow it to survive millions of years of river transport and erosion.
Field identification & locations
Identifiable in the field by its visible granular/crystalline texture, presence of glassy quartz grains alongside whitish/pinkish feldspar and dark amphibole/biotite, and its typical water-worn, rounded cobble form in riverbeds and beaches.
