metamorphic
Gneiss
Gneiss (Metamorphic Rock)
Hardness: 6-7 on Mohs scale; Color: Alternating light/dark bands (pink/white and black/green); Luster: Dull to vitreous; Structure: Foliated with distinct banding (gneissic foliation); Cleavage: None (fractures irregularly).
- Hardness
- 6-7 on Mohs scale
- Color
- Alternating light/dark bands (pink/white and black/green)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Alternating light/dark bands (pink/white and black/green); Luster: Dull to vitreous; Structure: Foliated with distinct banding (gneissic foliation); Cleavage: None (fractures irregularly).
Formation & geological history
Formed through high-grade regional metamorphism of igneous (granite) or sedimentary (shale/sandstone) protoliths under intense heat and pressure. The banded texture indicates recrystallization deep within the Earth's crust.
Uses & applications
Primarily used as a crushed stone in construction, road aggregates, and occasionally as dimension stone for countertops, flooring, and gravestones if it is particularly attractive.
Geological facts
Gneiss is among the oldest known rocks on Earth, with some specimens like the Acasta Gneiss dating back over 4 billion years. In Ohio, where this was found, it is commonly found as glacial till (erratic) transported by ice sheets from the Canadian Shield.
Field identification & locations
Identify in the field by its characteristic 'salty and pepper' banded appearance where minerals are segregated into layers. Common in glacial deposits in the Northern US. Look for coarse mineral grains and distinct stripes.
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