igneous
Granite River Cobble
Phaneritic Felsic Igneous Rock (Granite)
Hardness: 6-7 Mohs; Color: Speckled gray, white, and pinkish-orange; Luster: Dull (weathered) to vitreous (on fresh breaks); Texture: Phaneritic (visible crystals of quartz, feldspar, and biotite).
- Hardness
- 6-7 Mohs
- Color
- Speckled gray, white, and pinkish-orange
- Luster
- Dull (weathered) to vitreous (on fresh breaks)
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Physical properties
Hardness: 6-7 Mohs; Color: Speckled gray, white, and pinkish-orange; Luster: Dull (weathered) to vitreous (on fresh breaks); Texture: Phaneritic (visible crystals of quartz, feldspar, and biotite).
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). This specific specimen has been Rounded by fluvial or glacial erosion, likely over thousands of years.
Uses & applications
Commonly used as construction aggregate, decorative landscaping stone, and when polished, for countertops and monuments.
Geological facts
The pink/orange hues are caused by potassium feldspar (orthoclase), while the clear/gray glassy parts are quartz. Granite makes up the bulk of Earth's continental crust.
Field identification & locations
Identify by its interlocking 'salt and pepper' crystalline texture and extreme hardness. Often found in riverbeds, glacial tills, and mountain ranges.
