igneous
Granite River Pebble
Granite (composed of Quartz, Feldspar, and Biotite)
Hardness: 6-7 Mohs; Color: Mottled tan (feldspar), grey (quartz), and black (biotite/hornblende); Luster: Vitreous when wet or polished; Crystal structure: Phaneritic (coarse-grained)
- Hardness
- 6-7 Mohs
- Luster
- Vitreous when wet or polished
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled tan (feldspar), grey (quartz), and black (biotite/hornblende); Luster: Vitreous when wet or polished; Crystal structure: Phaneritic (coarse-grained)
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). This specimen appears water-worn, smoothed by transport in a river or coastal environment over thousands of years.
Uses & applications
Used in construction, countertops, monuments, and as decorative landscaping stone. Polished river pebbles are common in home decor and aquariums.
Geological facts
Granite is the primary component of the Earth's continental crust. The specific color of this specimen suggests a high concentration of orthoclase feldspar giving it the yellowish-tan tint.
Field identification & locations
Identify in the field by its speckled 'salt and pepper' appearance and extreme hardness (it will scratch glass). Commonly found in mountainous regions or riverbeds downstream from crystalline basement rocks.
