igneous
Weathered granite or granitic gneiss
Granite; primarily quartz, feldspar, and mica, with iron-oxide weathering
AI-generated identification · may be incorrectCoarse-grained, mottled tan-brown and gray, with a dull to vitreous luster and irregular fracture; typical hardness is about 6–7 Mohs and specific gravity 2.6–2.8. The granular texture suggests interlocking quartz and feldspar crystals, though strong weathering obscures them.
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Physical properties
Coarse-grained, mottled tan-brown and gray, with a dull to vitreous luster and irregular fracture; typical hardness is about 6–7 Mohs and specific gravity 2.6–2.8. The granular texture suggests interlocking quartz and feldspar crystals, though strong weathering obscures them.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in continental crust, generally during Precambrian to younger continental mountain-building events; the brown coloration results from surface oxidation and alteration of iron-bearing minerals.
Uses & applications
Used extensively as dimension stone, countertops, monuments, aggregate, and building material; this weathered fragment has mainly educational or decorative value.
Geological facts
Quartz is usually translucent gray, feldspar is white or tan, and mica appears as dark reflective flakes. Rusty staining commonly develops when biotite or other ferromagnesian minerals oxidize.
Field identification & locations
Identify it by its visible interlocking grains, lack of layers, hard resistant surface, and quartz-rich appearance; common worldwide in continental shields and mountain ranges. A fresh broken surface is more diagnostic than the weathered exterior.
