- 2059 Chaitra (old course) · 4 marks
Bedding versus foliation
Short answer
Bedding is primary layering in sedimentary rocks from depositional changes. Foliation is a secondary planar structure in metamorphic rocks, formed by alignment of minerals under directed pressure, which may cut bedding.
Differentiate between bedding and foliation.
| Point | Bedding | Foliation |
|---|---|---|
| Meaning | Layering of sedimentary rocks produced during deposition | Planar parallel arrangement of mineral grains in metamorphic rocks produced by pressure |
| Rock type | Sedimentary rocks | Metamorphic rocks (slate, phyllite, schist, gneiss) |
| Origin | Primary structure, formed at the time of deposition | Secondary structure, formed after the rock is formed |
| Cause | Changes in sediment type, grain size, colour or energy of deposition | Directed (differential) stress and recrystallisation |
| Planes | Bedding planes separate beds of different composition | Planes of alignment of platy minerals (mica), often perpendicular to maximum stress |
| Relation with original layers | Follows the original horizontal layering | May cut across original bedding |
| Examples | Sandstone, shale, limestone | Slaty cleavage, schistosity, gneissic banding |
✓ Answer checked by Claude Opus 5.5 (high effort)
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