igneous
Granite (River-worn Cobble)
Phaneritic Felsic Igneous Rock (primarily Quartz, Potassium Feldspar, and Plagioclase)
Hardness: 6-7 Mohs scale. Color: Mottled pink (orthoclase feldspar), white (plagioclase), and black (biotite/amphibole). Luster: Dull to vitreous. Structure: Phaneritic (visible crystals). Cleavage: Varies by mineral constituent. Specific Gravity: 2.63 to 2.75.
- Hardness
- 6-7 Mohs scale
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs scale. Color: Mottled pink (orthoclase feldspar), white (plagioclase), and black (biotite/amphibole). Luster: Dull to vitreous. Structure: Phaneritic (visible crystals). Cleavage: Varies by mineral constituent. Specific Gravity: 2.63 to 2.75.
Formation & geological history
Formed through the slow cooling of silica-rich magma deep underground (plutonic). This specific specimen shows significant rounding, indicating it was transported and abraded by water in a high-energy environment like a river or glacial stream.
Uses & applications
Used extensively in construction (countertops, flooring, monuments), as crushed stone for road base, and as decorative landscaping (river rocks).
Geological facts
Granite makes up a large portion of the Earth's continental crust. Because of its hardness and resistance to weathering, it often survives long-distance transport in rivers while softer rocks disintegrate.
Field identification & locations
Identify in the field by its 'salt and pepper' appearance with pink/orange hues and interlocking crystal texture. Common in continental shield areas or mountainous regions. Collectors look for unique mineral inclusions or high-polish potential.
