igneous
Granite
Phaneritic plutonic rock (SiO2 range 65-75%)
Hardness: 6-7 on Mohs scale; Color: Pink, white, gray, and black speckles; Luster: Vitreous to dull; Crystal structure: Phaneritic (large, visible grains); Cleavage: Indistinct (breaks irregularly); Specific Gravity: 2.65-2.75
- Hardness
- 6-7 on Mohs scale
- Color
- Pink, white, gray, and black speckles
- Luster
- Vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Pink, white, gray, and black speckles; Luster: Vitreous to dull; Crystal structure: Phaneritic (large, visible grains); Cleavage: Indistinct (breaks irregularly); Specific Gravity: 2.65-2.75
Formation & geological history
Formed through the slow crystallization of magma below Earth's surface. These specimens are likely glacial erratics or river-tumbled stones from the Precambrian to Cenozoic eras, reshaped by water erosion.
Uses & applications
Extensively used in construction (countertops, tiles), as dimension stone for monuments, and as crushed stone for road bases.
Geological facts
Granite makes up much of the Earth's continental crust. The pink color in these specific pebbles comes from orthoclase feldspar, while the black spots are typically biotite or hornblende.
Field identification & locations
Identify by its 'salt and pepper' appearance and hardness (cannot be scratched by a steel knife). Commonly found in mountainous regions or riverbeds downstream from igneous outcrops.
