Schist and gneiss
Topic: Minerals, Rocks and the Rock Cycle · NCERT: Beyond NCERT
Meaning
Schist and gneiss are two foliated metamorphic rocks. Foliated means their minerals have lined up in layers under pressure. Schist is medium-grained and full of flaky mica, which makes it shiny and lets it split into thin layers. It forms from shale, which changes to slate, then phyllite, then schist. Gneiss (said "nice") is coarse-grained. It shows light and dark bands, called banding, and it often forms from granite. Both are common in India's oldest rocks, the Archaean system.
Example
The Peninsular Gneiss at Lalbagh, Bengaluru, Karnataka, is a GSI National Geological Monument. The Archaean rocks of Bundelkhand also include the Bundelkhand gneiss.
Don't confuse with
- Granite: granite is igneous, and its crystals are scattered randomly. Gneiss is metamorphic, and its minerals are arranged in bands.