igneous
Granite Cobble
Granite (Phaneritic Igneous Rock)
Hardness: 6-7 (Mohs scale); Color: Salt and pepper (white, grey, and black); Luster: Dull to vitreous for mineral grains; Texture: Phaneritic (coarse-grained visible crystals); Density: 2.63 to 2.75 g/cm³; Composition: Quartz, Feldspar, and Biotite/Amphibole.
- Hardness
- 6-7 (Mohs scale)
- Color
- Salt and pepper (white, grey, and black)
- Luster
- Dull to vitreous for mineral grains
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Salt and pepper (white, grey, and black); Luster: Dull to vitreous for mineral grains; Texture: Phaneritic (coarse-grained visible crystals); Density: 2.63 to 2.75 g/cm³; Composition: Quartz, Feldspar, and Biotite/Amphibole.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground. This specific specimen is a water-worn river cobble, smoothed by mechanical weathering and transport over thousands of years.
Uses & applications
Used in construction as crushed stone or gravel, dimension stone for countertops and monuments, and as decorative garden mulch or landscaping material.
Geological facts
Granite is the primary rock of Earth's continental crust. Because it is resistant to acid rain and durable, it is the most popular material for tombstones and outdoor memorials.
Field identification & locations
Identify in the field by its distinctive 'speckled' look of interlocked crystals. It is ubiquitous in mountainous regions and riverbeds across all continents. Collectors find them in almost any glacial or fluvial deposit.
