metamorphic
Gneiss
Gneiss (Foliated Metamorphic Rock)
Mohs hardness around 6 to 7. Light to medium gray color with distinct dark and light mineral banding (gneissic foliation). Dull to pearly luster on fresh surfaces, fine to medium-grained texture, composed primarily of quartz, feldspar, and micas.
Identified More metamorphic →
Explore Gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Mohs hardness around 6 to 7. Light to medium gray color with distinct dark and light mineral banding (gneissic foliation). Dull to pearly luster on fresh surfaces, fine to medium-grained texture, composed primarily of quartz, feldspar, and micas.
Formation & geological history
Formed through regional metamorphism of igneous (like granite) or sedimentary rocks under high temperatures and high pressures deep within Earth's crust. Commonly associated with mountain-building events.
Uses & applications
Used as a crushed stone in construction, road base, aggregate, and occasionally as dimension stone, flagstone, or landscaping material.
Geological facts
The term 'gneiss' comes from an old German mining word meaning 'sparkling' or 'bright'. The alternating light and dark bands are created by mineral segregation during intense metamorphic compression.
Field identification & locations
Look for distinct parallel banding of alternating dark (biotite/amphibole) and light (quartz/feldspar) minerals. Frequently found in glaciated riverbeds, gravel pits, and metamorphic shield regions worldwide.
More like this
