igneous
Granitic Gravel Piece
Granite (Felsic Plutonic Rock / SiO2 with Al2O3, K2O, Na2O)
Hardness: 6-7 (Mohs scale); Color: Mottled cream, white, and dark grey; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible interlocking crystals); Specific gravity: 2.63 - 2.75.
- Hardness
- 6-7 (Mohs scale)
- Color
- Mottled cream, white, and dark grey
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Mottled cream, white, and dark grey; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible interlocking crystals); Specific gravity: 2.63 - 2.75.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). This process can occur over millions of years, often dating back to the Precambrian or Paleozoic eras, later exposed by erosion.
Uses & applications
Commonly used in construction aggregate, road base, and landscaping gravel. As a larger slab, granite is prized for countertops and ornamental stone.
Geological facts
Granite makes up a large portion of the Earth's continental crust. Because it is highly resistant to acid rain and weathering, it has been used since ancient times for monuments, including the Great Pyramid of Giza's burial chamber.
Field identification & locations
Identify by its 'salt and pepper' appearance of interlocking light (quartz/feldspar) and dark (biotite/hornblende) minerals. Found globally in mountain ranges and eroded shield areas. It will not react with vinegar (differentiating it from limestone).
