metamorphic
Gneissic Granite (River Stone)
Protomylonite or Gneiss
Hardness: 6-7 (Mohs scale), Color: Mottled gray, white, and black, Luster: Dull to slightly vitreous, Structure: Foliated or lineated with flattened mineral grains, Cleavage: Poor, Specific Gravity: 2.6-2.8
Identified More metamorphic →
Explore Gneissic Granite (River Stone) 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: Mottled gray, white, and black, Luster: Dull to slightly vitreous, Structure: Foliated or lineated with flattened mineral grains, Cleavage: Poor, Specific Gravity: 2.6-2.8
Formation & geological history
Formed through the regional metamorphism of igneous granite or sedimentary protoliths under high temperature and pressure. This specific specimen has been further shaped and smoothed by fluvial (river) or glacial erosion.
Uses & applications
Crushed stone for road beds, landscaping, architectural accents, and occasionally as a decorative worrying stone.
Geological facts
This specimen shows clear signs of 'foliation,' where intense pressure has aligned the mineral crystals into bands or streaks. While it started as a deep-earth rock, its rounded shape tells a story of travel through water over thousands of years.
Field identification & locations
Identify in the field by its hardness (will scratch glass), striped or streaked appearance, and smoothed, rounded edges if found near water. Common in mountainous regions or glacial till areas.
