igneous
Red Granite
Phaneritic Felsic Intrusive Igneous Rock (primarily K-feldspar, Quartz, and Biotite)
Hardness: 6-7 Mohs; Color: Pinkish-red (from Potassium Feldspar) with black specks (Biotite/Hornblende); Luster: Vitreous to dull when weathered; Structure: Phaneritic (coarse-grained, visible crystals); Specific gravity: 2.63 to 2.75.
- Hardness
- 6-7 Mohs
- Luster
- Vitreous to dull when weathered
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Physical properties
Hardness: 6-7 Mohs; Color: Pinkish-red (from Potassium Feldspar) with black specks (Biotite/Hornblende); Luster: Vitreous to dull when weathered; Structure: Phaneritic (coarse-grained, visible crystals); Specific gravity: 2.63 to 2.75.
Formation & geological history
Formed through the slow cooling of silica-rich magma deep within the Earth's crust (plutonism). Red granites frequently date back to the Precambrian or Paleozoic eras and are often associated with continental crust stable interiors.
Uses & applications
Extensively used as dimension stone for architecture, countertops, and grave markers due to durability. In smaller forms, it is used as decorative landscaping gravel, railroad ballast, or polished as pocket stones.
Geological facts
The red hue is specifically caused by a high concentration of orthoclase (potassium feldspar). If the feldspar is stained by trace amounts of hematite (iron oxide), the red color becomes even more vibrant.
Field identification & locations
Identify in the field by its 'salt and pepper' look but with a red/pink base; it will scratch glass and lacks bedding planes. Commonly found in the Canadian Shield, Scotland, and the Llano Uplift in Texas.
