igneous
Granite (Pegmatitic)
Phaneritic Felsic Igneous Rock
Hardness: 6-7 (Mohs scale); Color: Mottled tan, pink, white, and grey with black flecks; Luster: Vitreous to pearly; Crystal structure: Macro-crystalline (phaneritic); Cleavage: Perfect on feldspar grains; Specific gravity: Approx. 2.65-2.75.
- Hardness
- 6-7 (Mohs scale)
- Color
- Mottled tan, pink, white, and grey with black flecks
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Mottled tan, pink, white, and grey with black flecks; Luster: Vitreous to pearly; Crystal structure: Macro-crystalline (phaneritic); Cleavage: Perfect on feldspar grains; Specific gravity: Approx. 2.65-2.75.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep within the Earth's crust (plutonic formation). This specimen shows large grain sizes characteristic of pegmatitic environments or slow-cooling continental crust environments ranging from the Precambrian to Cenezoic eras.
Uses & applications
Used widely in construction (countertops, tiles, paving), as industrial aggregate, and occasionally in lapidary for polished decorative stones.
Geological facts
Granite makes up much of the Earth's continental crust. Unlike basalt which covers ocean floors, granite is buoyant and 'floats' on the more dense mantle. The Mount Rushmore carvings are made of a similar granite composition.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and mica. It is extremely common in mountainous regions and shield areas like Canada or Scandinavia. Collectors look for large shiny mica flakes or distinct pink potassium feldspar crystals.
