igneous
Granodiorite / Diorite (Weathered River Pebble)
Intrusive felsic-to-intermediate igneous rock
AI-generated identification · may be incorrectMohs hardness: 6 to 7; Color: mottled salt-and-pepper pattern of creamy white, grey, and dark green/black; Luster: dull to vitreous; Texture: phaneritic, crystalline with visible fractures and stream weathering; Specific gravity: ~2.65 - 2.80.
- Hardness
- 6 to 7
- Luster
- dull to vitreous
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Physical properties
Mohs hardness: 6 to 7; Color: mottled salt-and-pepper pattern of creamy white, grey, and dark green/black; Luster: dull to vitreous; Texture: phaneritic, crystalline with visible fractures and stream weathering; Specific gravity: ~2.65 - 2.80.
Formation & geological history
Formed by slow cooling and crystallization of intermediate to felsic magma deep within the Earth's crust (plutonic). Later exposed through erosion, fractured by tectonic stress, and rounded by water transport in a river or coastal setting.
Uses & applications
Commonly crushed for construction aggregate, road base, and riprap; when extracted in large sound blocks, used as dimension stone, countertops, and facing material. This weathered pebble has mainly educational or novelty value.
Geological facts
Rocks of this composition, including granodiorite and diorite, form a major component of volcanic arc roots and mountain belt batholiths, such as the Sierra Nevada Batholith in North America. The dark patches represent clusters of ferromagnesian minerals like amphibole (hornblende) or biotite.
Field identification & locations
Recognized by its interlocking crystalline texture containing both light plagioclase/quartz and darker mafic minerals, crossed by distinct structural micro-fractures. Found widely in glaciated terrains, gravel pits, and riverbeds draining crystalline mountain ranges.
