igneous
Granite with Hematite staining
Granitoid (Quartz, Feldspar, Mica) with Iron Oxide (Fe2O3)
Hardness: 6-7 Mohs; Color: Salt and pepper (white, gray, pink) with dark reddish-maroon staining; Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained); Specific Gravity: 2.6-2.7
- Hardness
- 6-7 Mohs
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (white, gray, pink) with dark reddish-maroon staining; Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained); Specific Gravity: 2.6-2.7
Formation & geological history
Formed by the slow crystallization of magma below Earth's surface. The reddish color is secondary weathering or staining caused by the oxidation of iron-bearing minerals or external mineralized water contact.
Uses & applications
Used extensively in construction (curbstones, decorative walls, countertops), monuments, and as crushed stone for road bases.
Geological facts
Granite makes up a large part of the Earth's continental crust. Pure granite is never red; red hues come from high potassium feldspar content or, as seen here, iron oxide staining.
Field identification & locations
Identify by the visible interlocking crystals of quartz and feldspar; the red surface is a topical stain that doesn't penetrate the whole rock. Commonly found in batholiths and mountain ranges.
