igneous
Granite Cobble
Granite (Felsic Intrusive)
Hardness (Mohs scale): 6-7. Color: Salt-and-pepper (white, grey, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (visible interlocking crystals of quartz, feldspar, and biotite). Cleavage: None (fractures irregularly). Specific gravity: 2.63 - 2.75.
- Color
- Salt-and-pepper (white, grey, and black)
- Luster
- Dull to vitreous
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Physical properties
Hardness (Mohs scale): 6-7. Color: Salt-and-pepper (white, grey, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (visible interlocking crystals of quartz, feldspar, and biotite). Cleavage: None (fractures irregularly). Specific gravity: 2.63 - 2.75.
Formation & geological history
Formed through the slow crystallization of magma below the Earth's surface. This specific specimen is a 'cobble,' meaning it was once part of a larger formation but was eroded and smoothed by water transport (likely in a river or on a beach).
Uses & applications
In bulk: construction, road base, and architectural granite (countertops). As a cobble: landscaping and decorative garden stone.
Geological facts
Granite is the most common rock found in the Earth's continental crust. Because it is highly resistant to acid rain and mechanical wear, it preserves glacial scratches and polishing well in nature.
Field identification & locations
Identify in the field by its 'speckled' appearance and high hardness (it cannot be scratched by a steel knife). Look for it in riverbeds, glacial moraines, or mountainous regions where tectonic activity has uplifted deep-seated igneous rocks.
