The origin of clay
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The origin of clay

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    The origin of clay The origin of clay Presentation Transcript

    • 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
    • How are clays formedClays are formed from weathering of silica rich rocks e.g GraniteProcesses 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 basicallyby 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 ROCKSCoarse Grains-slow coolingClays are not formed from Extrusive rocks
    • Diorite
    • Granite
    • Granite pegmatite
    • Gabbro
    • Mechanisms of clay mineralsformation -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 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/ inheritance neoformatio transformati environment n on s sedimentary weathering Diagenesis- hydrothermal
    • CONTROVERSIAL ISSUE OFDETRITAL 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 vsDiagenesis 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 RICHSHALES -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
    • 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 ONGROUPS -KAOLINITE -MONTMORILLIONITE -SMECTITE -ILLITE -CHLORITE
    • BASED ON GENERALCOMPOSITION 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
    • 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 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