Cleavage. Rock cleavage or cleavage –tendency of rock to break along surfaces of a specific orientatio; all cleavages are foliations .

1. CLEAVAGE
ASHIKRAJ RS

2. CLEAVAGE
• Rock cleavage or cleavage –tendency of rock to break along surfaces of a specific
orientation; all cleavages are foliations.
• A tendency to split along planes other than bedding. Cleavage is directly linked to other
deformation processes- especially folding- and metamorphism. It can help in understanding the
fold geometry and the physical conditions during deformation. It may serve as a conduit for
ground water.
• Cleavage – A prominent planar structure that may differ in orientation from the bedding
and indicate subsequent deformation and metamorphism

3. SPECIAL TYPES OF CLEVAGES
• Recommended for Field descriptions; no genetic implications.
• Microliths – Uncleaved zones between cleavage surfaces
• Mainly four types- Slaty Cleavage, Phyllitic Cleavage, Schistosity
(increase in grain size from the first to third, with plenty of platy
minerals) and gneissic foliation (platy minerals not abundant)
• Slaty Cleavage- fine continuous foliations-slates-breaks easily along
foliation-weathers preferentially.
• Phyllitic Cleavage- resembles slaty cleavage but grain size slightly
coarser-in hand specimens the foliation surface has a sheen-
intermediate between fine and coarse continuous foliation- strongly
influence weathering.

4. S-SURFACES
• S-Surface – All planar and some curved structures in
deformed rocks
• i.e. Cleavage, foliations, and bedding
• S0 – Oldest surface, S1 – next oldest, etc.
• Fold Sets – F1, F2, etc.
• Linear Structures – L1, L1, etc.
• Deformation Structures – D1, D2, etc.

5. Foliations
and
Cleavage
Spaced
Compositional Diffuse
Banded
Disjunctive Stylolitic
Anastomosing
Rough
Smooth
Crenulation Zonal
Discrete
Continuous
Fine Microcrenulation
Microdisjunctive
Microcontinuous
Coarse Mineral grain
Discrete
Morphological Classification scheme for foliations –Source: Twiss and Moores (2003) p.298

6. CLEAVAGE BEDDING RELATIONSHIP
The angular relationship between cleavage and
bedding can be used to determine whether
one is observing the upright or the
overturned limb of a fold.
If bedding dips less steeply (lower angle but
same direction as cleavage) the rock will be
on upright limb.
Care should be taken regarding the fold axis
and timing of cleavage.

7. CLEAVAGE REFRACTION
 Refraction of cleavage from layer to layer occurs where the
texture and composition-ductility- vary from layer to layer in
rocks. The angle between cleavage and bedding changes or
refracts as the cleavage passes from one layer to another.
 Most slaty cleavage forms parallel to axial surfaces in folds but
may be displaced or fanned with respect to the hinge as folding
proceeds

8. DIFFERENT SCALES OF CLEVAGE

9. REFERENCE
• Twiss, R. J and Moores, E. M (2007) Structural Geology, W.H. Freeman and
Company, New York, pp.297-307
• Hobbs B. E., Means W. D., and Williams P. F (1976) An Outline of Structural
Geology, John Wiley & Sons, Inc., New York, pp.267-288

10. • THANKS