igneous
Granite Pebble (River Rock)
Granite (composed primarily of Quartz, Feldspar, and Mica)
Hardness: 6-7 on Mohs scale; Color: Mottled gray, white, and brown; Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained internally, though surface is water-worn); Specific Gravity: 2.63 to 2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled gray, white, and brown
- Luster
- Dull to vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled gray, white, and brown; Luster: Dull to vitreous; Structure: Phaneritic (coarse-grained internally, though surface is water-worn); Specific Gravity: 2.63 to 2.75.
Formation & geological history
Formed through the slow crystallization of magma below Earth's surface. This specific specimen has been further shaped by fluvial (river) erosion, rounding its edges over thousands of years.
Uses & applications
River rocks of this type are used extensively in landscaping, drainage systems, construction aggregate, and as decorative elements in gardens.
Geological facts
Granite is the most common igneous rock found on Earth's continents. The mottling seen here is due to the different mineral crystals (Quartz, Feldspar, and Biotite) cooling at different rates.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance and extreme hardness (it will scratch glass). Commonly found in riverbeds, glacial tills, and mountainous regions.
