igneous
Granodiorite River Pebble
Granodiorite
Hardness: 6-7 (Mohs scale), Color: light gray with dark speckles (salt and pepper appearance), Luster: dull to vitreous on fresh surfaces, Structure: phaneritic (visible crystals), Cleavage: poor, Specific Gravity: 2.6-2.7
Identified More igneous →
Explore Granodiorite River Pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale), Color: light gray with dark speckles (salt and pepper appearance), Luster: dull to vitreous on fresh surfaces, Structure: phaneritic (visible crystals), Cleavage: poor, Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic) before being unearthed and rounded by fluvial erosion in a riverbed.
Uses & applications
Used in construction as crushed stone, road base, and dimension stone; also an interesting specimen for teaching river morphology and igneous petrology.
Geological facts
Granodiorite is intermediate between granite and diorite. It is the primary rock type of the Sierra Nevada batholith and was the stone used to carve the famous Rosetta Stone.
Field identification & locations
Identify by its coarse-grained texture and high proportion of light-colored plagioclase feldspar compared to potassium feldspar. Commonly found in riverbeds downstream from mountain ranges.
