igneous
Granodiorite (River Rock / Cobble)
Granodiorite; Phaneritic intrusive igneous rock dominated by plagioclase, quartz, and hornblende/biotite
Hardness: 6-7 on Mohs scale. Color: Mottled salt-and-pepper appearance with grey, black, and pinkish-white tones. Luster: Dull (weathered) to vitreous (broken surface). Texture: Phaneritic (medium to coarse-grained crystals).
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull (weathered) to vitreous (broken surface)
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled salt-and-pepper appearance with grey, black, and pinkish-white tones. Luster: Dull (weathered) to vitreous (broken surface). Texture: Phaneritic (medium to coarse-grained crystals).
Formation & geological history
Formed from the slow cooling of silica-rich magma beneath the Earth's surface (plutonic). This specific specimen has been smoothed and rounded by long-term transport in water (fluvial or glacial processes).
Uses & applications
Used primarily in construction as crushed stone, road base, and decorative landscaping. High-quality slabs are sometimes used for countertops ('granite').
Geological facts
Granodiorite is geographically widespread and makes up a significant portion of the Earth's continental crust. It is the rock type that makes up the famous Rosetta Stone.
Field identification & locations
Identify in the field by its visible interlocking crystals and the presence of more white/grey plagioclase than pink potassium feldspar. Commonly found in riverbeds, glacial tills, and mountain ranges.
