CLASSIFICATION, STRUCTURE, CHEMICAL COMPOSITION AND PROPERTIES OF CLAY MINERAL I & II.pptx

Soil clays can exist in crystalline, structurally disordered or amorphous form.

Amorphous : has no recognizable shape or geometrical internal arrangement of atoms

Crystalline: atomic arrangement repeated at regular pattern in 3 dimensional directions

spatial arrangement of atoms producing building unit of a crystal is called the unit cell

By placing several unit cells together, the crystal arrangement produced is then called a lattice structure

unit cells has a volume of approximately 1µm3

packing of silica tetrahedran and aluminum octahedran sheets, forms a layered clay structure
the total assembly of a layer plus interlayer material is called an unit structure

1. CLASSIFICATION, STRUCTURE, CHEMICAL COMPOSITION AND PROPERTIES OF CLAY MINERAL I & II Presented by BARATHKUMAR S M.Sc. (Ag.) Soil science TNAU, COIMBATORE

2. Structural chemistry of clay minerals Soil clays can exist in crystalline, structurally disordered or amorphous form. Amorphous : has no recognizable shape or geometrical internal arrangement of atoms Crystalline : atomic arrangement repeated at regular pattern in 3 dimensional directions spatial arrangement of atoms producing building unit of a crystal is called the unit cell By placing several unit cells together, the crystal arrangement produced is then called a lattice structure unit cells has a volume of approximately 1µm 3 packing of silica tetrahedran and aluminum octahedran sheets, forms a layered clay structure the total assembly of a layer plus interlayer material is called an unit structure

3. Based on the arrangement of SiO4 It is classified into 6 types 1. Cyclosilicates—Closed rings or double rings of tetrahedra (SiO3, Si2O5) 2. Inosilicates—Single or double chains of tetrahedra (SiO3,Si4O11) 3. Nesosilicates—Separate SiO4 tetrahedra 4. Phyllosilicates—Sheets of tetrahedra (Si2O5) 5. Sorosilicates —Two or more linked tetrahedra (Si2O7, Si5O16) 6. Tectosilicates—Framework of tetrahedra (SiO2)

4. Major Types of Soil minerals 1) crystalline silicate clays 2) non-crystalline silicate clays 3) Fe/Al oxides (non silicate clays)

5. The predominant type of colloids in most soils is the crystalline silicate type. These colloids have a layered structure-phyllosilicates. Each layer consists of two to four sheets of closely packed and tightly bonded O 2 , Si, and Al atoms. Their structure make them negatively charged. Members of this group differ in particle shape, and adsorption of water and ions. Examples = Kaolinite , smectite , mica, etc 1. Crystalline silicate mineral

6. General Structure of Crystalline silicate mineral ( 2 main building blocks ) Single silica tetrahedral structure Single Al/Mg Octahedral structure Silica tetrahedral sheet Al octahedral sheet

7. Connecting the tetra and octa building blocks to form planes of Si and Al (Mg) ions that alternate with planes of O 2 and OH ions.

8. number and sequence of tetrahedral and octahedral sheets layer charge per unit cell of structure type of interlayer bond and inter layer cations cations in the octahedral sheet type of stacking arrangement along the 'C' dimension Layer silicate minerals are differentiated by

9. On the basis of number of tetrahedral & octahedral sheets in one layer, the following structural types are recognized 1:1 or dimorphic eg. kaolinite 2:1 or trimorphic eg. Smectite 2:2 (or) 2:1:1 (or) tetramorphic types eg. chlorite 1:1 – kaolinite - 1 octahedral and 1 tetrahedral sheet 2:1 – montmorillonite - 2 tetrahedral to 1 octahedral sheet 2:2 – chlorite - 2 tetrahedral to 2 octahedral sheet 2:1:1 - Polygorskite and sepiolite

10. Structural unit is formed by arrangement of a tetrahedral sheet upon an octahedral sheet Apical oxygen's of the tetrahedral sheet are shared by octahedral sheet, forming a common plane of oxygen ions within the structure In the shared plane, two thirds of the oxygen ions are shared between Si and Al, remaining one third oxygen ions have their charge satisfied by H + to form OH - groups upper surface is a layer of closely packed OH groups but the bottom surface is composed of hexagonally open packed oxygen's and OH groups placed within hexagenal (ditrigonal) openings Eg : Kaolinite – Al 2 Si 2 O 5 (OH) 4 or Al 4 Si 4 O 10 (OH) 8 1:1 Layer silicates

11. 1:1 layer clays a. Kaolinite They are hydrated alumino silicates with a chemical composition Al 2 O 3 :SiO 2 : H 2 O (or) 2SiO 2 .Al 2 O 3 . 2H 2 O. per unit cell. Members are kaolinite , dickite , nackrite and halloysite isomers of kaolinite : Dickite and nacrite Except halloysite , other minerals are non expandable in water. Imporatnt minerals : 1. Dioctahedral eg . Kaolinite 2.Trioctahedral eg . Serpentine minerals, chrysolite , greenalite It widely distributed in soils It is important fraction of clay in Ultisols and Oxisols detected as accessory minerals in Alfisols and Vertisols in the tropics has a triclinic symmetry and often occurs as crystals with hexagonal shape little isomorphic substitution and the permanent charge per unit cell is very small. Has low plasticity, shrinkage and swelling properties

12. Its lesser surface area (7-30 m 2 /g) limits the adsorption capacity of cations CEC is very small in the range of 1-10 m.eq /100g. structure of the mineral involves hydrogen bonding between adjacent layers spaced at intervals of 7.2A°. presence of hydrogen bonding prevents the expansion of kaolinite beyond its basal spacing in water or other organic liquids

13. Structure No water molecules

14. b. Halloysite Structure is similar to kaolinite except a layer of water is hydrogen bonded between 1:1 silicate layers. water molecules are attached to the adjacent silica and alumina sheets by hydrogen bonding. fully hydrated halloysite – Si 4 Al 4 O 10 -(OH) 8 .4H 2 O is also known as Eindellite (or) hydrated halloysite . Halloysite readily dehydrates to give 7.2 to 7.6A° basal spacing occurs very commonly in soils In acid conditions it is present in soil clays of well-weathered soils, eg. : Humic latosols of Hawaii .

15. Structure

16. Sheet like halloysite is called tubular halloysite and has been detected in the soils of Texas can be considered as a precursor of kaolinite – formation of the mineral follows the weathering sequence. igneous rock montmorillonite halloysite metahalloysite kaolinite has very little or no isomorphous substitutions in 1:1 layers. occurs in soils of volcanic origin ( eg. In the soils of Andept suborder)

17. structural unit is formed by One octahedral sheet sandwiched between, and sharing oxygen atoms with two tetrahedral sheets . unit layers are stacked parallel to each other in the "C" dimension eg. Pyrophyllite : Al 2 Si 4 O 10 (OH) 2 (or) Al 4 Si 8 O 20 (OH) 4 2:1 Type layer silicate

18. 1. Talc- phyro phyllite group 2:1 layer clays 2. Mica group di and tri octahedral members there is no isomorphous substitution Mg ions occupy all the octahedral positions in talc Al 3+ occupy 2 out of each three octahedral positions in pyrophyllite very rarely occurs in soils , inherited from low grade metamorphic rocks Eg . Talc : Mg 3 Si 4 O 10 (OH) 2 Pyrophyllite : Al 2 Si 4 O 10 (OH) 2 consists of negatively charged layers one fourth of Si ions in the tetrahedral sheet replaced by Al ions leading to an excess negative charge

19. 2:1 layer clays (Expanding) a. Smectite Minerals in this group are formerly called ‘ montmorillonite ’ and have a variable composition. formula : Al 2 O 3 .4SiO 2. H 2 O+ xH 2 O Name smectite or montmorillonite is also often referred as bentonite Eg . Beidellite and Nontronite has Mg and ferric ions in octahedral positions Bedillite contains no Mg or Fe in the octahedral sheet and characterized by high Al content. silicate layer charge is derived entirely by substitution of Al 3+ for Si 4+ Nontronite is like smectite but all Al 3+ replaced by Fe 3+ In trioctahedral subgroup : only two members are recognized : hectorite and saponite Most soil smectites (montmorillonites) are dioctahedral. Members : Montmorillonite , Beidelite , Saponite , Nontronite , Hectorite

20. b. Montmorillionite formed by weathering of basic rocks and ashes under poor drainage conditions spacing of the layers ranges from 12 to 18A°. One Al octahedral sheet is sandwiched between 2 Si tetrahedral sheets crystal layers are stacked together in random fashion bonds holding the layers together are relatively weak , developing intermicellar spaces that will expand with increasing moisture content. CEC is 70 meq/100g for montmorillonite specific surface area is approximately 700 to 800m 2 /g (large surface area) which is exposed on dispersion in water montmorillonite exhibits strong plasticity and stickiness

21. minerals are generally very fine grained basal spacing of montmorillonite increases uniformly with adsorption of water high swell-shrink potential is the reason that the mineral can admit and fix metal ions and organic compounds adsorption of organic compounds leads to formation of organo mineral complexes Organic ions able to replace inorganic cations in the interlayer position are characteristic constituents of clays of vertisols , Mollisols Alfisols and Entisols high plasticity and swell shrink potential of the mineral make these soils plastic when wet and hard when dry.

22. II. Non expanding types a. Illite poorer in K and rich in OH and H 3 O + other names are bravacite , hydromica, hydromuscovite , hydrous mica, hydroglimma widespread mineral in sediments formed by the alteration of mica minerals or by anthogenic processes from weathering products of other minerals more or less resistant to weathering are of secondary origin has similar chemical composition as muscovite, but contains more SiO 2 and less K

23. contains inter layer K, thus unit layers are bonded stronger together than montmorillonite CEC is 30 meq /100g plasticity, swelling and shrinking are less intense in illite intermicellar spaces of illite do not expand upon addition of water physical properties are closer to kaolinite than montmorillonite characterized by a basal spacing of 10.0 AO important constituent of clays in Mollisol , Spodosols, Alfisols , Aridisols , Inceptisols and Entisols soils affected by high precipitation : mineral tends to be altered into montmorillonite under the influence of warmer climates or higher temperatures: the structure of illite is reported to become more disordered and kaolinite is formed

24. Structure of illite

25. b. Vermiculite Mg rich mica mineral expanded to 14A° because of strong hydration of the interlayered Mg cation coarse mineral, not wide spread formed by hydrothermal action on biotite in Mg rich environment When erosion occurs the mineral is also formed like biotite in the clay fraction of glacial sediments exfoliates when strongly heated - due to H 2 O vapour molecules between the layers, volume is there by increased up to 16 times and become porous It is commercially used as a soil conditioner and an insulator of sound and heat buildings.

26. Vermiculite divided into two categories true vermiculite clay vermiculite is not considered as a clay mineral clay size vermiculite found in soils but a rock – forming mineral is considered “clay vermiculite’ or soil vermiculite Having largest CEC among inorganic colloids CEC is 150 meq /100 g and exceeds that of montmorillonite . CEC of dioctahedral vermiculite is 1.05 times higher than trioctahedral vermiculite High selectivity for fixation of K and NH 4 + and other cations , high K + and NH 4 + fixation values in many soils are attributed more to the presence of vermiculite than to montmorillonite or illite type of clays. occurs as accessory mineral in the clay fractions of Ultisols , Mollisols and Aridisols formed more in well-drained soils , in contrast to montmorillonite which requires gley condition for formation

27. c. Illite Minerals consists of layers of two (Si:Al)–O tetrahedral sheets enclosing one Al (Mg , Fe) – OH Octahedran sheet. layers are linked by K, Ca, Mg or Na cations Eg: muscovite, hydrous muscovite, illite, non-illite, expanded illite, glauconite, k- bentonite, biotite, vermiculite weather to 2:1 layer phyllosilicates such as Vermiculite and smectite with a release of inter layer K ions. Dioctohedral micas (muscovite) are more resistant to weathering while the trioctahedral micas (biotite) less resistant to weathering. Mica minerals are rock forming components but in sediments they are also wide spread. Apart from magnetic origin (muscovite, biotite), a large amount of anthogenic origin also found in soil sediments.

28. is rich in Al common in rocks contain less K than illite but have some H 3 O well pronounced cleavage due to weathering action plates are often bent, which frequently causes interference effects. Muscovite This coarse, Fe, Mg, rich mica mineral found in many kinds of rocks in varying amount. As a result of erosion it may also occurs in the clay fraction of glacial sediments. Biotite

29. Muscovite Biotite

30. closely related to micas and has same layer charge interlayer potassium of mica is replaced by a positively charged Octahedral "brucite" Mg 3 (OH) 6 sheet brucite sheet develops a positive charge when Mg 2+ is partially replaced by Al 3+ replacement is often 1/3 rd of the Mg 2+ positions to given the basic unit Mg 2 Al (OH) 6 +1 that fits into the interlayer position of 2:1 layer silicates to yield the 2:1:1 type classification chlorites are non expanding with low CEC and are generally trioctahedral 2:1:1 or 2: 2 type layer silicate

31. 2:1:1 or 2:2 layer clays Chlorites structure consists of a mica like layer which carries excess negative charge are hydrated Mg and Al silicates which are related to mica minerals Structurally related to talc or 2:1 layer clays shows close relationship with vermiculate composed of Mg (OH)2 are sandwiched between the two silica tetrahedral sheets intermicellar spaces are also occupied by brucite sheets Isomorphic substitution occur in both tetrahedral and octahedral layer. Based on the Fe / R ratios, three group of chlorite are recognized: Fe- chlorites – containing relatively high Fe, high Fe/R ratio Intermediates Mg- chlorites – contain smaller amounts of Fe, small Fe/R ratio has only very small charge and so less CEC detected as accessory minerals in clays of Alfisols , Mollisols and Aridisols .

32. Interstratified clays or Mixed layer clays Under specific conditions, two and less commonly three (or even four) distinct alumino silicate clays were formed and stacked along the c-axis Such interstratification leads to the formation of mixed layer or interstratified minerals regular stratified minerals : stacked regularly irregular inter stratification : stacked irregularly Irregular inter stratification is more commonly found in soil clays Under hydrothermal or metamorphic condition the formation of regular interstratified mineral occurs Inter stratification processes are: partial removal of interlayer K ions from micas / illites or of interlayer hydroxides from chlorite interlayer fixation of K ion by some vermiculite layers to yield mica / illite formation of hydroxide interlayer to form chlorite like structuresChlorite – smectite Eg: Chlorite – vermiculite, Mica-vermiculite

33. Mixed layer clays

34. These clays consist of tightly bonded O 2 , Si, and Al atoms, but they do not have ordered, crystalline sheets. Examples = Allophane, imogolite These group of colloids are highly charged, and are formed from volcanic ash. 2. Noncrystalline silicate minerals

35. Non crystalline Amorphous clays amorphous materials may have great specific surface high AEC and CEC greatly influence the chemistry of the soil no sharp distinction between amorphous and crystalline materials various degrees of crystallinity can occur during the reorganization of hydrous gels Eg : Allophane, Imogolite "Amorphous" is usually defined as being non detectable by "X' ray diffraction, and those while lack orderly arrangement of atoms / unit cells

36. Allophane gives a porous stable structure, with high permeability / leaching. have a high CEC ranging from 10-150 m e/100 g and the CEC is highly dependent on pH and degree of hydration. high surface area of 70 - 300 m2/g (70-300 x 103 m2/kg) which also varies widely with degree of crystallinity and pH. high Al and Fe activity of allophone cause a problem of high "P fixation" capacity in soils. Imogolite Consists of gibbsite sheet with isolated Si ions bridging three O ions over the vacant octahedral sheet Co ordination of Si ions is completed with OH ions Allophane

37. 3. Iron and Aluminum Oxides These colloids are found in highly weathered tropical environments. They consist of Fe, Mn, and Al atoms in coordination with O 2 atoms. Fe and Al oxides group of colloids consist of crystalline sheets. But there are some members in the group that may not be crystalline. Their net charge range from slightly –ve to moderately +ve.

38. Structure of Oxide colloids These are octahedral sheets with either Fe or Al in the cation positions. They do not have tetrahedron sheets, and they do not have Si in their structure. They do not have isormorphous substitution. Eg. Gibbsite [Al(OH) 3 ]shown here. Other examples are Goethite (FeOOH), Hematite [Fe 2 O 3 ], etc.

39. Oxides Hematite Fe 2 O 3 Magnetite Fe 3 O 4 Rutile TiO 2 Illmanite FeTiO 2 Hydroxides Gibbsite Al (OH) 3 Geothite r Fe O-OH Lepidocrosite r Fe O-OH Sulphite Pyrites FeS 2 Sulphate Gypsum CaSO 4 . 2H 2 O Chlorides Halite NaCl Carbonates Calcite CaCO 3 Dolomite CaMgCO 3 Phosphates Apatite Ca 3 (CaF, CaCl) PO 4 Vivianite Fe 3 (PO 4 ) 2 8 H 2 O Nitrate Sodanitre NaNO 3 Non-silicates

40. Iron and aluminum hydrous oxide clays do not belong to the phyllosilicates but are oxides of Fe and Al, containing associated water Two major forms of crystalline monohydrates of ferric oxide : goethite and lepidocrocite anhydrous ferric oxides : Hematite and Maghemite Composition of Fe and Aluminum oxide minerals Fe oxide minerals Aluminum oxide minerals Goethite - FeOOH Diaspore - AlOOH Lepidocricite - FeOOH Boehmite - AlOOH Hematite - Fe 2 O 3 Gibbsite Al(OH) 3 Maghemite - Fe 2 O 3 Ferrihydrite Fe 5 HO 8 .4H 2 O or Fe 5 (O 4 H 3 ) 3

41. Gibbsite [ Al(OH) 3 (or) Al 2 O 3 .3H 2 O] : is the most abundant free hydrous oxide of alumina in soils of Tropical and Sub tropical regions. Intensive weathering of Feldspars, and minerals with heavy leaching of silica, results in the formation of aluminum hydroxide Boehmite [ AlOOH ]: hydroxy aluminium oxide have the aluminium ions octa hedrally co- ordinated by O and OH ions. These occur in intensively weathered and leached soils, frequently in association with gibbsite. Diaspore : [ AlOOH ]: isomer of boehmite is a crystal structural analogue of geothite . These are involved in low temperature hydro thermal action - occurs in some alumninous five clay deposits. Corundum [AlO 3 ]: It is a high temperature product of Al-oxides, rarely found in soils Aluminium Oxides

42. Hematite : [Fe 2 O 3 ]. - most common iron oxides in soils, gives pink to bright red colour to soils. ii . Geothite : [ FeOOH ] Gives brown and dark reddish brown colours to soils, provide an extremely important reflects of the chemical properties, tend to occur as amorphous coatings gradually transforming to crystalline forms as the quantity increase. iii. Martite : [Fe 2 O 3 ] An isomer of Heamtite having a structure very similar to Hematite. iv. Limonite [Fe2O 3 . 3H 2 O] : It is an isomer of geothite reported to present in poorly drained organic soils occurring as "bog ores" giving bright orange colour to soils v . Magnetite [Fe 3 O 4 ] Magnetic iron oxide of spinal structure inherited from parent rock. Occurs in soils as sand size mineral. Dark in colour and abundant in "black sands" of beach oxidation of Fe in Fe 3 O 4 yields Maghemite [Fe 3 O 4 ] Iron Oxides

43. Comparative properties of important clay minerals Property Montmrillonite Illite Kaolinite Structure 2:1 lattice 2:1 lattice 1:1 lattice Substitution Substitution in octahedral sheet by mg or Fe Substitution in tetrahedral sheet by Al No Substitution Size (microns) 0.01 – 1.0 0.10 – 2.0 0.1 – 5.0 Shape Irregular flakes Irregular flakes Hexagonal crystals Surface area (m2/g) 700-800 10-120 5-20 Cohesion, plasticity and swelling capacity high medium low External/Internal surface Very high medium Not at all CEC ( Cmol (P + ) kg -1 ) 80-100 15-40 3-15 AEC( Cmol (P + ) kg -1 ) low medium high

44. CEC of some clay minerals Minerals CEC (meq/100g) Kaolinite 3-15 Halloysite (2 to 4 H 2 O) 5-50 Montmorillonite 80-150 Illite 10-40 Chlorite 10-40 Vermiculate 100-150

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