metamorphic
Gneiss and Igneous Rock Collection
Foliated Metamorphic Rock (Gneiss) / Igneous Rocks
Hardness: 6-7 on Mohs scale. Colors range from grayish-brown to dark gray and tan with distinct coarse-grained banding and speckling. Dull to earthy luster, phaneritic and foliated textures.
- Hardness
- 6-7 on Mohs scale
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Physical properties
Hardness: 6-7 on Mohs scale. Colors range from grayish-brown to dark gray and tan with distinct coarse-grained banding and speckling. Dull to earthy luster, phaneritic and foliated textures.
Formation & geological history
Formed under high-temperature and high-pressure regional metamorphism of pre-existing igneous or sedimentary rocks deep within continental crust.
Uses & applications
Used in construction as crushed stone, dimension stone for paving and building facades, and as landscape rock or educational collection specimens.
Geological facts
Gneiss is one of the oldest rock types on Earth; the Acasta Gneiss in Canada is around 4.03 billion years old, making it one of the oldest known intact crustal rocks.
Field identification & locations
Look for visible alternating light and dark bands (gneissic banding) or granular interlocking mineral grains. Commonly found in shield regions, mountain belts, and riverbeds.
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