igneous
Granite Glacial Erratic
Phaneritic Plutonic Felsic Rock (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8 – SiO2)
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (mottled grey, white, and black). Luster: Dull (weathered) to vitreous (fresh break). Structure: Massive, phaneritic (visible coarse grains). Cleavage: Imperfect. Specific Gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt-and-pepper (mottled grey, white, and black)
- Luster
- Dull (weathered) to vitreous (fresh break)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (mottled grey, white, and black). Luster: Dull (weathered) to vitreous (fresh break). Structure: Massive, phaneritic (visible coarse grains). Cleavage: Imperfect. Specific Gravity: 2.63 to 2.75.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). This specific specimen appears to be a glacial erratic, transported by ice sheets during the Pleistocene epoch and rounded by glacial/fluvial abrasion.
Uses & applications
Used widely in construction for countertops, floor tiles, and paving stones. In its raw form, it is used for riprap, road base, and as decorative landscaping boulders.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Because it is so resistant to weathering, large boulders like this one can remain on the surface for thousands of years after being deposited by retreating glaciers.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and mica. It will not be scratched by a steel knife. Commonly found in mountainous regions or glacial till plains.
