Transcript THE ORIGIN OF CLAY

But why clayIt is important to know where we are coming from ,
since the course of study in MNA/IMACS centers on
clay and clay minerals basically
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 Carbonates
Requirements
 - ReactionTime
 - Igneous Rocks (Intrusive Igneous Rocks)
 -Geological Factor
 -Agents of Transportation
 Agents of Weathering
 -Alteration of Chemical composition
 -Pressure
 -Temperature
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 clay
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 feldspar
SOME INTRUSIVE ROCKS
Coarse Grains-slow cooling
Clays are not formed from Extrusive rocks
Diorite
Granite
Granite pegmatite
Gabbro
Mechanisms of clay minerals
formation
 -Inheritance
 -Neoformation
 -Transformation
 The 3 mechanisms operating in 3 geological systems
 -Weathering
 -Sedimentary
- Diagenetic hydrothermal
Inheritance
 Another area reaction
 Stable
 Natural deposit
 Previous stage in rock cycle reaction
 Dominace in sedimentary environments
Neoformation
 Clays precipitation from solution
 Reaction of amorphous material
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 ground
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 environments
The best mechanism
 Layer transformation
 Result of this type of reaction are better preserved in
geological records
Environment of formation
 1)Weathering zone
 Upper zone of the earth crust –T and P varies
 Short reaction time
 2)Sedimentary environment-long reaction
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time(sedimentation,subsidence)
-near or below sea level
Sediment-water interface
-low temperature
Pressure (1 kb )
 Diagenetic hydrothermal
 -zones in contact with hot water
 -wide range of environmental conditions
Incresing energy required
Mechnism/
environment
s
sedimentary
weathering
Diagenesishydrothermal
inheritance
neoformatio
n
transformati
on
CONTROVERSIAL ISSUE OF
DETRITAL VS DIAGENESIS
 ORIGIN OF CLAYS
 DETRITAL OR DIAGENESIS
 Detrital-reflection of character of source material,
inheritance of basic clay mineral lattice
 Diagenesis-adsorption of cation and its modification
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
occur
XRD OF ORGANIC AND PYRITE RICH
SHALES
 -No particular clay mineral is restricted to a particular
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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 monomineralic
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
TYPES OF CLAYS BASED ON
GROUPS
 -KAOLINITE
 -MONTMORILLIONITE
 -SMECTITE
 -ILLITE
 -CHLORITE
BASED ON GENERAL
COMPOSITION AND PROPERTIES
 -KAOLIN-consist mainly of kaolinite
 -BENTONITE-majorly monmorillionite,hardens when
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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-attapulgite
Bibliography
 Clay mineral formation and transformation in rocks
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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 Directory
 NOW THAT WE KNOW WHERE WE ARE COMING
FROM , WE CAN IDENTIFY WHERE WE ARE
GOING TO
 THANKS FOR LISTENING
 MERCI POUR VOTRE ATTENTION