igneous
Granite river rock
Granite (composed of Quartz, Feldspar, and Mica)
Hardness: 6-7 Mohs; Color: Gray with salt-and-pepper black and white speckles; Luster: Dull (weathered) to vitreous; Crystal structure: Phaneritic (visible crystals); Specific gravity: 2.63-2.75
- Hardness
- 6-7 Mohs
- Color
- Gray with salt-and-pepper black and white speckles
- Luster
- Dull (weathered) to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Gray with salt-and-pepper black and white speckles; Luster: Dull (weathered) to vitreous; Crystal structure: Phaneritic (visible crystals); Specific gravity: 2.63-2.75
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface. This specific specimen has been smoothed and rounded by long-term water erosion in a river or creek bed.
Uses & applications
Used in construction, gravel, landscaping, and as a decorative stone. High-quality granite is used for countertops and monuments.
Geological facts
Granite makes up a large portion of the continental crust. The black spots in this specimen are likely biotite mica or hornblende, while the light areas are quartz and feldspar.
Field identification & locations
Identify by its speckled 'salt and pepper' appearance and extreme hardness (cannot be scratched by a steel knife). Commonly found in riverbeds, glacial tills, and mountain ranges.
