igneous
Weathered granite (granite cobble)
Granite, chiefly quartz, feldspar, and mica; dark vein likely mafic mineral concentration or iron-oxide-stained fracture
AI-generated identification · may be incorrectCoarse-grained, speckled tan-gray rock with granular texture, dull to slightly vitreous luster, and no obvious cleavage as a whole; constituent feldspar is Mohs 6, quartz Mohs 7. The dark linear zone appears to be a weathered fracture or possible narrow mafic vein.
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Physical properties
Coarse-grained, speckled tan-gray rock with granular texture, dull to slightly vitreous luster, and no obvious cleavage as a whole; constituent feldspar is Mohs 6, quartz Mohs 7. The dark linear zone appears to be a weathered fracture or possible narrow mafic vein.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in continental crust, commonly during Precambrian to Phanerozoic mountain-building events; this specimen was later uplifted and rounded by weathering or transport.
Uses & applications
Used extensively as dimension stone, countertops, monuments, aggregate, and decorative landscaping stone; attractive pieces are collected but generally have little gem value.
Geological facts
Granite is an intrusive igneous rock whose visible grains record slow underground cooling. Brown coloration commonly results from oxidation of iron-bearing minerals or staining along fractures.
Field identification & locations
Identify it by visible interlocking quartz and feldspar grains, commonly with black mica or amphibole; a glassy streak suggests quartz, while feldspar is typically opaque and blocky. Common worldwide, especially in continental shields and mountain belts.
