Igneous or Metamorphic
Granite or Granitic Gneiss River Rock
Granite / Gneiss
Hardness: 6-7, Color: Gray, tan, and black mottling, Luster: Dull (weathered) to somewhat shiny depending on mineral grains, Crystal structure: Granular, interlocking, Cleavage: None for the rock as a whole
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Physical properties
Hardness: 6-7, Color: Gray, tan, and black mottling, Luster: Dull (weathered) to somewhat shiny depending on mineral grains, Crystal structure: Granular, interlocking, Cleavage: None for the rock as a whole
Formation & geological history
Formed from the slow cooling of magma deep underground (granite) or the metamorphism of pre-existing rocks (gneiss). The rounded shape is due to fluvial (river) transport and weathering.
Uses & applications
Used in landscaping, construction aggregate, and hardscaping.
Geological facts
River rocks are shaped by the continuous tumbling and abrasion caused by flowing water, which smooths out their rough edges over time.
Field identification & locations
Identify by its rounded shape, mottled appearance indicating different mineral grains (quartz, feldspar, mica), and hardness. Commonly found in riverbeds, glacial till, and landscaping deposits.
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