igneous
Red Granite
Felsic Plutonic Rock (Potassium Feldspar Granite)
Hardness: 6-7 on Mohs scale; Color: Red, pink, and gray mottled; Luster: Vitreous to dull; Crystal structure: Phaneritic (visible crystals); Cleavage: Perfect in feldspar grains; Specific gravity: 2.63–2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Red, pink, and gray mottled
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Red, pink, and gray mottled; Luster: Vitreous to dull; Crystal structure: Phaneritic (visible crystals); Cleavage: Perfect in feldspar grains; Specific gravity: 2.63–2.75
Formation & geological history
Formed by the slow cooling and crystallization of silica-rich magma deep underground, typically during the Proterozoic or Paleozoic eras. The red color is due to high concentrations of potassium feldspar (orthoclase) and iron oxide inclusions.
Uses & applications
Commonly used in construction for countertops, monuments, and floor tiles. It is also a popular specimen for collectors and lapidary work.
Geological facts
The red granite found in the El Paso, Texas region (31.7°N) is often associated with the Franklin Mountains, which contain Precambrian Red Bluff Granite that is approximately 1.1 billion years old.
Field identification & locations
Identify in the field by checking for interlocking visible crystals of pink/red feldspar, translucent quartz, and dark biotite or hornblende. It will not scratch with a steel knife but can scratch glass. This aligns well with the Texas/New Mexico border geology.
