CLAYS But why clay It is important to know where we are coming from since the course of study in MNAIMACS centers on clay and clay minerals basically How are clays formed Clays are formed from weathering of silica rich rocks ID: 239890
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Slide1
THE ORIGIN OF CLAYS
But why clay-
It is important to know where we are coming from , since the course of study in MNA/IMACS centers on clay and clay minerals basicallySlide2
How are clays formed
Clays are formed from weathering of silica rich rocks
e.g
Granite
Processes of Formation-
-Weathering of the silica rich rock
-bedrock weathering
-transporting of the weathered rocks
-Sedimentary processes
-Incorporation of CarbonatesSlide3
Requirements
-
ReactionTime
- Igneous Rocks (Intrusive Igneous Rocks)
-Geological Factor
-Agents of Transportation
Agents of Weathering
-Alteration of Chemical composition
-Pressure
-TemperatureSlide4
Types of Clays –Based on Origin
1-Residual Clays-not far from parent rock
2-Sedimentary Clays -far from parent material
Residual Clay (primary clays)–Non
plastic,white,e.g
kaolin
Sedimentary Clay (secondary clays)-
Plastic,grey,darker,smaller
paricles
and uniform
e.g
ball
clay,fire
claySlide5
Residual clays are formed basically by surface weathering
This gives clays in 3 ways
-chemical decomposition of rocks
-solution of rocks(limestone)containing clayey impurities which are insoluble
-
disintergration
and solution of
shales
But the most common process of clay formation is the
decompostion
of feldsparSlide6
SOME INTRUSIVE ROCKS
Coarse Grains-slow cooling
Clays are not formed from Extrusive rocksSlide7
DioriteSlide8
GraniteSlide9
Granite pegmatiteSlide10
GabbroSlide11
Mechanisms of clay minerals formation
-Inheritance
-
Neoformation
-Transformation
The 3 mechanisms operating in 3 geological systems
-Weathering
-Sedimentary
-
Diagenetic
hydrothermalSlide12
Inheritance
Another area reaction
Stable
Natural deposit
Previous stage in rock cycle reaction
Dominace
in sedimentary environmentsSlide13
Neoformation
Clays precipitation from solution
Reaction of amorphous materialSlide14
Neoformation
Secondary precipitates of calcite ,
sulphates
, Fe
Affirmation of permafrost
Structural and mineralogical changes are irreversible and affect present soils
Understanding of
quartenary
environment-needs assessment of possible frozen groundSlide15
Transformation
Possesion
of inherited structure
Chemical reactions-ions exchanged and modification of
cations
(layer transformation)
1)ion exchange between
losely
bound ion and those of environments
2)layer transformation –modification of arrangement of octahedral, tetrahedral and interlayer
cations
Dominance in
diagenetic
-hydrothermal environmentsSlide16
The best mechanism
Layer transformation
Result of this type of reaction are better preserved in geological recordsSlide17
Environment of formation
1)Weathering zone
Upper zone of the earth crust –T and P varies
Short reaction time
2)Sedimentary environment-long reaction time(
sedimentation,subsidence
)
-near or below sea level
Sediment-water interface
-low temperature
Pressure (1 kb )Slide18
Diagenetic
hydrothermal
-zones in contact with hot water
-wide range of environmental conditionsSlide19
Incresing energy required
Mechnism
/
environments
inheritance
neoformation
transformation
sedimentary
weathering
Diagenesis
-hydrothermalSlide20
CONTROVERSIAL ISSUE OF DETRITAL VS DIAGENESIS
ORIGIN OF CLAYS
DETRITAL OR DIAGENESISSlide21
Detrital
-reflection of character of source material, inheritance of basic clay mineral lattice
Diagenesis
-adsorption of
cation
and its modificationSlide22
Application of XRD in Detrital
vs
Diagenesis
controversy
-Collection of thousands of samples
-to illustrate the variety of clay under similar environmental conditions
-variety of environments in which same clay minerals occurSlide23
XRD OF ORGANIC AND PYRITE RICH SHALES
-No particular clay mineral is restricted to a particular environments
-dominance of
kaolinite
in
fluviate
environment
-
illite
,
monmorillionite
abundance,frequency,sole
clay mineral in all environments
-
chlorite
not a dominant mineral
-non marine
shales
are
seldom,if
ever
monomineralicSlide24Slide25Slide26Slide27Slide28
interpretation
-clay minerals do not originate from depositional environments
-they are
detrital
in origin
-though they are altered(degraded) in
fluviate
and
subaerial
environments
But little evidence of alteration in major basin of deposition to show that it is a major factor in defining the ultimate
mineralogic
character of clay Slide29
TYPES OF CLAYS BASED ON GROUPS
-KAOLINITE
-MONTMORILLIONITE
-SMECTITE
-ILLITE
-CHLORITESlide30
BASED ON GENERAL COMPOSITION AND PROPERTIES
-KAOLIN-consist mainly of
kaolinite
-BENTONITE-majorly
monmorillionite,hardens
when mixed with water
-BALL CLAY-
kaolinite
, mica
-FIRE CLAY-
kaolinite
,
feoxide,magnesia,alkalines,can
resist high temp
-COMMON CLAY-no resistance to heat, has impurities than fire clay
-ARMENIAN BOLE-
attapulgiteSlide31
Bibliography
Clay mineral formation and transformation in rocks and soils by D.D EBERL , US Geological survey
A discussion on the origin of clay minerals in sedimentary rocks by Charles .E Weaver, Shell Oil
Co,Houston,Texas
Identification of Clay minerals by
Xray
Diffraction Analysis by George W
Brindley
The origin of clay minerals in
soilsand
weathered rocks,
www.springer.com
Clay types, geologic origins by ARTS
186 DirectorySlide32
NOW THAT WE KNOW WHERE WE ARE COMING FROM , WE CAN IDENTIFY WHERE WE ARE GOING TOSlide33
THANKS FOR LISTENING
MERCI POUR VOTRE ATTENTION