igneous
Granite (Alkali-feldspar Granite)
Felsic Plutonic Rock (Primary minerals: Quartz SiO2, Orthoclase KAlSi3O8, Plagioclase (Na,Ca)AlSi3O8)
Hardness: 6-7 Mohs; Color: Pinkish-red, white/clear, and dark grey; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained/visible crystals); Cleavage: None in quartz, perfect in feldspar; Specific gravity: 2.63 - 2.75
- Hardness
- 6-7 Mohs
- Color
- Pinkish-red, white/clear, and dark grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Pinkish-red, white/clear, and dark grey; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained/visible crystals); Cleavage: None in quartz, perfect in feldspar; Specific gravity: 2.63 - 2.75
Formation & geological history
Formed through the slow cooling and crystallization of silica-rich magma deep within the Earth's crust (plutonic). Found in continental tectonic plates; often Proterozoic or Paleozoic in age for surface exposures.
Uses & applications
Used extensively in construction for countertops, floor tiles, and gravel. It is also a popular material for monuments, sculptures, and as a decorative landscaping stone.
Geological facts
Granite makes up the majority of Earth's continental crust. Mount Rushmore is carved into a giant granite formation in the Black Hills. Pink hues are specifically caused by high concentrations of potassium feldspar (orthoclase).
Field identification & locations
Identify in the field by looking for a 'salt and pepper' or interlocking crystalline texture where common minerals like quartz and feldspar are visible to the naked eye. Found in mountain ranges and glacial deposits worldwide.
