igneous
Granodiorite (River Pebble)
Granodiorite
Hardness: 6-7 (Mohs); Color: Mottled grey, white, and black; Luster: Dull (weathered) to vitreous; Structure: Phaneritic (medium-grained crystalline); Cleavage: None (fractures irregularly). Heavy and dense.
- Hardness
- 6-7 (Mohs)
- Color
- Mottled grey, white, and black
- Luster
- Dull (weathered) to vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Mottled grey, white, and black; Luster: Dull (weathered) to vitreous; Structure: Phaneritic (medium-grained crystalline); Cleavage: None (fractures irregularly). Heavy and dense.
Formation & geological history
Formed from the slow cooling of silica-rich magma beneath the Earth's surface. This specific specimen has been further shaped by fluvial (river) erosion, which smoothed its edges over hundreds to thousands of years.
Uses & applications
Used primarily as crushed stone for road construction, building materials, and as decorative river rock in landscaping.
Geological facts
Granodiorite is the main component of many famous mountain ranges and was the material used to carve the Rosetta Stone. It has more plagioclase feldspar than orthoclase, distinguishing it from true granite.
Field identification & locations
Look for a salt-and-pepper appearance with interlocking crystals and a rounded, smooth surface if found near water. It is very common in glacial till and riverbeds across North America.
