igneous
Granitoid (Granite/Diorite)
Course-grained Plutonic Igneous Rock
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled grey, black, and tan); Luster: Dull to vitreous; Structure: Phaneritic (visible crystals); Cleavage: Distinct in feldspar grains; Specific gravity: ~2.6-2.8
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (mottled grey, black, and tan)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled grey, black, and tan); Luster: Dull to vitreous; Structure: Phaneritic (visible crystals); Cleavage: Distinct in feldspar grains; Specific gravity: ~2.6-2.8
Formation & geological history
Formed through the slow cooling and crystallization of magma deep beneath the Earth's surface (plutonic formation). This specimen shows rounding and smoothing, indicating it was likely transported by water in a river or coastal environment.
Uses & applications
Used widely in construction as crushed stone, dimension stone for countertops and flooring, and occasionally in landscaping as river rock.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Because it cools slowly underground, individual mineral crystals such as quartz, feldspars, and micas have time to grow large enough to be seen with the naked eye.
Field identification & locations
Identify by its interlocking 'salt and pepper' crystalline texture and extreme hardness (cannot be scratched by a steel knife). Commonly found in mountain ranges and as rounded cobbles in glacial till or riverbeds.
