This presentation discusses briefly the differences between foliation and lineation, showing the main types of primary foliation and secondary foliation and how to identify them.

1. Structural Geology
By: Ahmed Essam

2. Principles
▰ Non-Tectonic structures:
Also called primary structures
which formed without the
influence of any tectonic
forces.
▰ Tectonic Structures:
A l s o c a l l e d s e c o n d a r y
structures which formed due to
tectonic movements and
activities.
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3. Some Basic concepts
▰ Structure: the geometric
form or shape in rocks with
s c a l e r a n g e f r o m
m i c r o s c o p i c t o l a r g e
regional scale.
▰ T e x t u r e : p r e f e r e d
o r i e n t a t i o n o f
crystallographic axes in 3
dimensions.
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4. Some Basic Concipts
▰ Mico-structure: small scale
arrangement of geometric
forms of minerals within a
rock usually formed due to
external forces or extreme
conditions.
▰ F a b r i c : a g e o m e t r i c
c o n f i g u r a t i o n a n d
a r r a n g e m e n t o f r o c k
elements or components
large enough to be seen in
many samples.
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5. Some Basic Concipts
▰ Foliation: a general term
for any planner fabric in a
rock.
▰ Lineation: a general term to
describe any repeated
a l i g n m e n t o f l i n e a r
elements in a rock.
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6. Foliation Vs. Lineation
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7. Some Basic Concipts
▰ Cleavage: a secondary
fabric element formed
under low temperature
conditions which depends
on rock tendency to split
along planes.
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8. Primary Structure : Foliation
▰ B e d d i n g : t h i s w o r d
indicates a sedimentary
origin which in the original
states sedimentary rocks
are formed and found in a
horizontal pattern not
affected by any tectonic
forces.
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9. Primary Structure : Foliation
▰ Prefered orientation of
Bubbles: characterizes
some types of igneous
extrusive rocks especially "
Pumice fragments ".
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10. Primary Structure : Foliation
▰ Prefered orientation of
clasts: usually charactrizes
clastic sedimentary rocks
which oriantation occurs
d u e t o s e d i m e n t a r y
processes during deposition.
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11. Primary Structure : Foliation
▰ M a g m a t i c l a y e r i n g :
characterizes cumulate
magmatic rocks.
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12. Secondary Structure : Foliation
▰ Secondary foliation: this
type of structures forms
under faverable conditions
of temperature or pressure
o r b o t h , d u e t o s u c h
deformation processes
some mineralogical and
geometric changes may
o c c u r a n d e v e n n e w
minerals may grow.
▰ Secondary foliation usually
divided into to main types:
A. Continuous.
B. Spaced.
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13. Secondary Structure : Foliation
▰ Spaced Foliation:
A. Disjunctive Cleavage.
1. Styolitic.
2. Anastomosing.
3. Rough.
4. Smooth.
A. Crenulation Cleavage.
▰ Continuous Foliation:
1. Pencil Cleavage.
2. Slaty Cleavage.
3. Phyllite structure.
4. Schistosity.
5. Gneissic layering and Migmatization.
6. Mylonitic Foliation.
7. Flattened pebbles. 13
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14. Secondary Structure : Foliation
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15. Spaced Foliation : Disjunctive
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16. Disjunctive : Styolitic
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17. Disjunctive : Anastomosing
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18. Spaced Foliation : Crenulation
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19. Morphological Classification
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20. Continuous Foliation
▰ P e n c i l s t r u c t u r e :
characterizes fine grained
sedimentary rocks like
shales and mudstones
which breaks into elongate
pencil-like shards.
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21. Continuous Foliation
▰ S l a t y c l e a v a g e :
characterizes very low
g r a d e r e g i o n a l
metamorphic rocks which
consists of parallel grains
of chay minerals like
chlorite or mica forming
thin layers.
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22. Pencil Vs. Slaty Cleavage
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23. Continuous Foliation
▰ P h y l l i t i c s t r u c t u r e :
characterizes low grade
metamorphic rocks which
is a continuous cleavage
with a distinctive silky
luster.
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24. Continuous Foliation
▰ Schistosity: characterizes
l o w t o m e d i u m g r a d e
m e t a m o r p h i c r o c k s ,
shcistosity tends to be wavy
as mica curves around the
large crystals.
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25. Continuous Foliation
▰ Gneissic layering and
Migmatization: formed due
to recrystallization of
igneous or sedimentary
rocks during medium, high
a n d v e r y h i g h g r a d e
metamorphism.
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26. Contunuous Foliation
▰ F l a t t e n e d - p e b b l e s :
c h a r a c t e r i z e s
m e t a m o r p h o s e d
c o n g l o m e r a t e s a n d
pyroclastic rocks which
contain pancake-shaped
pebbles arranged parallel to
each other.
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27. Continuous Foliation
▰ M y l o n i t i c F o l i a t i o n :
characterized by grain sizes
have been reduced as a
result of intensive shearing
as ductilely deformed rocks
by the accumulation of
large shear strain in ductile
fault zones.
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28. Mylonite Classification
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29. Thanks
E-mail: geo.ahmedessam@gmail.com
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