igneous
Granite cobble
Granite (composed primarily of Quartz, Feldspar, and Mica)
Hardness: 6-7 Mohs; Color: Speckled pink, gray, and white with iron-oxide staining; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: None for the rock, though feldspar grains within show cleavage.
- Hardness
- 6-7 Mohs
- Color
- Speckled pink, gray, and white with iron-oxide staining
- Luster
- Dull to vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Speckled pink, gray, and white with iron-oxide staining; Luster: Dull to vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: None for the rock, though feldspar grains within show cleavage.
Formation & geological history
Formed from the slow crystallization of magma below Earth's surface. High-grade metamorphic or igneous environments, often transport and polished by water or glacial activity as seen in this rounded cobble shape.
Uses & applications
Used extensively in construction (curbstones, aggregate), landscaping, and dimension stone for countertops.
Geological facts
Granite is one of the most common rocks in the Earth's continental crust and is incredibly resistant to erosion, which is why it is often found as smooth river stones or glacial erratics.
Field identification & locations
Identify in the field by its phaneritic texture (visible mineral grains) and high hardness (cannot be scratched by a steel blade). This specific specimen shows iron staining on the surface.
