igneous
Granite (River Pebble)
Phaneritic intrusive igneous rock (Felsic)
Hardness: 6-7 Mohs; Color: Mottled tan, cream, and dark grey/black; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals of quartz, feldspar, and mica); Specific gravity: 2.6-2.7.
- Hardness
- 6-7 Mohs
- Color
- Mottled tan, cream, and dark grey/black
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled tan, cream, and dark grey/black; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals of quartz, feldspar, and mica); Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground, typically within the Earth's continental crust. This specimen has been rounded and smoothed by water erosion in a river or stream environment.
Uses & applications
Large-scale construction, countertops, monuments, and decorative gravel. Small pebbles like this are used in landscaping or as aquarium decor.
Geological facts
Granite is the most common igneous rock found on Earth's continents. The pinkish-tan color in this specimen likely comes from potassium feldspar (orthoclase).
Field identification & locations
Identify by the 'salt and pepper' appearance of interlocking mineral grains and its high hardness (it will scratch glass). Commonly found in mountain ranges and riverbeds downstream from granitic plutons.
