1. But why clay- It is important to know where we are coming from ,since the course of study in MNA/IMACS centers onclay and clay minerals basically

2. How are clays formedClays are formed from weathering of silica rich rockse.g GraniteProcesses of Formation--Weathering of the silica rich rock-bedrock weathering-transporting of the weathered rocks-Sedimentary processes-Incorporation of Carbonates 3. Requirements - ReactionTime - Igneous Rocks (Intrusive Igneous Rocks) -Geological Factor -Agents of Transportation Agents of Weathering -Alteration of Chemical composition -Pressure -Temperature 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.gkaolin Sedimentary Clay (secondary clays)-Plastic,grey,darker,smaller paricles and uniform e.gball clay,fire clay 5. Residual clays are formed basicallyby surface weathering This gives clays in 3 ways -chemical decomposition of rocks -solution of rocks(limestone)containing clayeyimpurities which are insoluble -disintergration and solution of shales But the most common process of clay formation is thedecompostion of feldspar 6. SOME INTRUSIVE ROCKSCoarse Grains-slow coolingClays are not formed from Extrusive rocks 7. Diorite 8. Granite 9. Granite pegmatite 10. Gabbro 11. Mechanisms of clay mineralsformation -Inheritance -Neoformation -Transformation The 3 mechanisms operating in 3 geological systems -Weathering -Sedimentary - Diagenetic hydrothermal 12. Inheritance Another area reaction Stable Natural deposit Previous stage in rock cycle reaction Dominace in sedimentary environments 13. Neoformation Clays precipitation from solution Reaction of amorphous material 14. Neoformation Secondary precipitates of calcite , sulphates , Fe Affirmation of permafrost Structural and mineralogical changes are irreversibleand affect present soils Understanding of quartenary environment-needsassessment of possible frozen ground 15. Transformation Possesion of inherited structure Chemical reactions-ions exchanged and modificationof cations (layer transformation) 1)ion exchange between losely bound ion and those ofenvironments 2)layer transformation modification of arrangementof octahedral, tetrahedral and interlayer cations Dominance in diagenetic-hydrothermal environments 16. The best mechanism Layer transformation Result of this type of reaction are better preserved ingeological records 17. Environment of formation 1)Weathering zone Upper zone of the earth crust T and P varies Short reaction time 2)Sedimentary environment-long reactiontime(sedimentation,subsidence) -near or below sea level Sediment-water interface -low temperature Pressure (1 kb ) 18. Diagenetic hydrothermal -zones in contact with hot water -wide range of environmental conditions 19. Incresing energy requiredMechnism/inheritance neoformatio transformatienvironmentn onssedimentaryweatheringDiagenesis-hydrothermal 20. CONTROVERSIAL ISSUE OFDETRITAL VS DIAGENESIS ORIGIN OF CLAYS DETRITAL OR DIAGENESIS 21. Detrital-reflection of character of source material,inheritance of basic clay mineral lattice Diagenesis-adsorption of cation and its modification 22. Application of XRD in Detrital vsDiagenesis controversy -Collection of thousands of samples-to illustrate the variety of clay under similarenvironmental conditions-variety of environments in which same clay mineralsoccur 23. XRD OF ORGANIC AND PYRITE RICHSHALES -No particular clay mineral is restricted to a particularenvironments -dominance of kaolinite in fluviate environment -illite ,monmorillionite abundance,frequency,sole claymineral in all environments -chlorite not a dominant mineral -non marine shales are seldom,if ever monomineralic 24. interpretation -clay minerals do not originate from depositionalenvironments -they are detrital in origin -though they are altered(degraded) in fluviate andsubaerial environments But little evidence of alteration in major basin ofdeposition to show that it is a major factor in definingthe ultimate mineralogic character of clay 25. TYPES OF CLAYS BASED ONGROUPS -KAOLINITE -MONTMORILLIONITE -SMECTITE -ILLITE -CHLORITE 26. BASED ON GENERALCOMPOSITION AND PROPERTIES -KAOLIN-consist mainly of kaolinite -BENTONITE-majorly monmorillionite,hardens whenmixed with water -BALL CLAY-kaolinite, mica -FIRE CLAY-kaolinite, feoxide,magnesia,alkalines,canresist high temp -COMMON CLAY-no resistance to heat, hasimpurities than fire clay -ARMENIAN BOLE-attapulgite 27. Bibliography Clay mineral formation and transformation in rocksand soils by D.D EBERL , US Geological survey A discussion on the origin of clay minerals insedimentary rocks by Charles .E Weaver, Shell OilCo,Houston,Texas Identification of Clay minerals by Xray DiffractionAnalysis by George W Brindley The origin of clay minerals in soilsand weatheredrocks, www.springer.com Clay types, geologic origins by ARTS 186 Directory 28. NOW THAT WE KNOW WHERE WE ARE COMING FROM , WE CAN IDENTIFY WHERE WE ARE GOING TO 29. THANKS FOR LISTENING MERCI POUR VOTRE ATTENTION