igneous
Granite River Pebble
Phaneritic Felsic Igneous Rock (Granite)
Hardness: 6-7 Mohs; Color: Tan, brown, and grey with iron staining; Luster: Dull/Matte (due to weathering); Crystal Structure: Granular/Phaneritic; Specific Gravity: 2.6-2.7
- Hardness
- 6-7 Mohs
- Color
- Tan, brown, and grey with iron staining
- Luster
- Dull/Matte (due to weathering)
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Physical properties
Hardness: 6-7 Mohs; Color: Tan, brown, and grey with iron staining; Luster: Dull/Matte (due to weathering); Crystal Structure: Granular/Phaneritic; Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the slow cooling of magma deep underground, typically during the Precambrian or Paleozoic eras. These specific specimens have been rounded by water erosion in a fluvial (river) or glacial environment.
Uses & applications
Common landscape gravel, construction aggregate, and educational specimens for geology students.
Geological facts
Granite is the most common rock found in the Earth's continental crust. These rounded shapes are 'well-sorted' by water action, which eventually grinds them down into sand.
Field identification & locations
Identify in the field by the visible interlocking crystals of quartz and feldspar; the smooth, rounded 'potato' shape indicates transport by water. Found globally in riverbeds and glacial tills.
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