But why clay- It is important to know where we are coming from, since the course of study in...
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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 basically
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 basically
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 basically
Slide 2
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
Slide 3
Requirements - ReactionTime - Igneous Rocks (Intrusive Igneous
Rocks) -Geological Factor -Agents of Transportation Agents of
Weathering -Alteration of Chemical composition -Pressure
-Temperature
Slide 4
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
Slide 5
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
Slide 6
SOME INTRUSIVE ROCKS Coarse Grains-slow cooling Clays are not
formed from Extrusive rocks
Slide 7
Diorite
Slide 8
Granite
Slide 9
Granite pegmatite
Slide 10
Gabbro
Slide 11
Mechanisms of clay minerals formation -Inheritance
-Neoformation -Transformation The 3 mechanisms operating in 3
geological systems -Weathering -Sedimentary - Diagenetic
hydrothermal
Slide 12
Inheritance Another area reaction Stable Natural deposit
Previous stage in rock cycle reaction Dominace in sedimentary
environments
Slide 13
Neoformation Clays precipitation from solution Reaction of
amorphous material
Slide 14
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
Slide 15
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
Slide 16
The best mechanism Layer transformation Result of this type of
reaction are better preserved in geological records
Slide 17
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 )
Slide 18
Diagenetic hydrothermal -zones in contact with hot water -wide
range of environmental conditions
Slide 19
Incresing energy required Mechnism/ environment s
inheritanceneoformatio n transformati on sedimentary weathering
Diagenesis- hydrothermal
Slide 20
CONTROVERSIAL ISSUE OF DETRITAL VS DIAGENESIS ORIGIN OF CLAYS
DETRITAL OR DIAGENESIS
Slide 21
Detrital-reflection of character of source material,
inheritance of basic clay mineral lattice Diagenesis-adsorption of
cation and its modification
Slide 22
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
Slide 23
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
monomineralic
Slide 24
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Slide 28
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
Slide 29
TYPES OF CLAYS BASED ON GROUPS -KAOLINITE -MONTMORILLIONITE
-SMECTITE -ILLITE -CHLORITE
Slide 30
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-attapulgite
Slide 31
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.comwww.springer.com Clay types, geologic origins by
ARTS 186 Directory
Slide 32
NOW THAT WE KNOW WHERE WE ARE COMING FROM, WE CAN IDENTIFY
WHERE WE ARE GOING TO
