igneous
Granite Water-worn Cobble
Felsic intrusive igneous rock (Phaneritic)
Color: Pinkish-tan, grey, and white. Hardness: 6-7 on Mohs scale. Luster: Dull to vitreous. Structure: Phaneritic (medium-grained crystalline). Composition: Primarily quartz, potassium feldspar, and plagioclase.
- Hardness
- 6-7 on Mohs scale
- Color
- Pinkish-tan, grey, and white
- Luster
- Dull to vitreous
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Physical properties
Color: Pinkish-tan, grey, and white. Hardness: 6-7 on Mohs scale. Luster: Dull to vitreous. Structure: Phaneritic (medium-grained crystalline). Composition: Primarily quartz, potassium feldspar, and plagioclase.
Formation & geological history
Formed from the slow cooling of magma deep beneath the Earth's surface. This specific specimen has been smoothed and rounded by water erosion in a river, lake, or coastal environment.
Uses & applications
Large deposits are used for construction, countertops, and monuments; as a river pebble, it is used for landscaping and decorative garden features.
Geological facts
Granite makes up much of the Earth's continental crust. The pinkish hue in this specimen suggests a high concentration of potassium feldspar (orthoclase).
Field identification & locations
Identified by its 'salt and pepper' crystalline texture and extreme hardness (cannot be scratched by a steel knife). Commonly found in glacial till, riverbeds, and beaches worldwide.
