Clays are formed through the weathering of silica-rich rocks like granite. They require reaction time, igneous rocks, geological factors, transportation and weathering agents. There are two types of clays based on origin - residual clays form near the parent rock through chemical weathering, while sedimentary clays form farther away through sedimentary processes. The formation of clay minerals occurs primarily through three mechanisms: inheritance from the parent rock, neoformation through precipitation from solution, and transformation through chemical reactions like ion exchange. The environment of clay formation includes weathering zones, sedimentary environments, and diagenetic-hydrothermal zones.

1. 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

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

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.g
kaolin
 Sedimentary Clay (secondary clays)-
Plastic,grey,darker,smaller paricles and uniform e.g
ball clay,fire clay

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

6. SOME INTRUSIVE ROCKS
Coarse Grains-slow cooling
Clays are not formed from Extrusive rocks

7. Diorite

8. Granite

9. Granite pegmatite

10. Gabbro

11. Mechanisms of clay minerals
formation
 -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 irreversible
and affect present soils
 Understanding of quartenary environment-needs
assessment of possible frozen ground

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

16. The best mechanism
 Layer transformation
 Result of this type of reaction are better preserved in
geological 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 reaction
time(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 required
Mechnism/ inheritance neoformatio transformati
environment n on
s
sedimentary
weathering
Diagenesis-
hydrothermal

20. CONTROVERSIAL ISSUE OF
DETRITAL 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 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

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

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

29. TYPES OF CLAYS BASED ON
GROUPS
 -KAOLINITE
 -MONTMORILLIONITE
 -SMECTITE
 -ILLITE
 -CHLORITE

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

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.com
 Clay types, geologic origins by ARTS 186 Directory

32.  NOW THAT WE KNOW WHERE WE ARE COMING
FROM , WE CAN IDENTIFY WHERE WE ARE
GOING TO

33.  THANKS FOR LISTENING
 MERCI POUR VOTRE ATTENTION