igneous
Granite
Phaneritic intrusive igneous rock (Granite)
Hardness: 6-7 Mohs; Color: Salt and pepper (gray, white, black); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (fractures); Specific gravity: 2.63-2.75
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (gray, white, black)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (gray, white, black); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: None (fractures); Specific gravity: 2.63-2.75
Formation & geological history
Formed by the slow cooling of silica-rich magma deep underground (plutonic). Most granite dates from the Precambrian or Paleozoic eras. This specific specimen appears to be a glacial erratic or water-worn boulder.
Uses & applications
Extensively used in construction for countertops, floor tiles, paving stones, and monuments due to its durability and resistance to weathering.
Geological facts
Granite makes up a large part of the Earth's continental crust. It is one of the hardest natural stones in the world and has been used since ancient Egyptian times for building obelisks and pyramids.
Field identification & locations
Identify by the interlocking 'salt and pepper' grains of quartz, feldspar, and mica. Commonly found in mountainous regions or as rounded boulders in glacial till. Look for a speckled, non-porous surface that doesn't scratch easily with steel.
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