Phyllosilicates PDF

LAYER SILICATES  Called as phyllosilicate , ‘Phyllon’ in greek means leaf = flaky or platy habit. Also referred as sheet silicate  Abundant mineral in many environment- felsic igneous rocks, fine grained sedimentary rocks, in the metamorphic rocks equivalent to these compo...

LAYER SILICATES  Called as phyllosilicate , ‘Phyllon’ in greek means leaf = flaky or platy habit. Also referred as sheet silicate  Abundant mineral in many environment- felsic igneous rocks, fine grained sedimentary rocks, in the metamorphic rocks equivalent to these compositions.  Common within 20 km of earth’s surface  All are hydrous STRUCTURE  Structure contain two different types of layers- Octahedral layer (O) and Tetrahedral layer (T).  In tetrahedral layer 3 of the oxygens are Shared with neighbouring Tetrahedra. Si:O=2:5  The octahedral layers take on the structure of either Brucite [Mg(OH)2], if the cations are +2 ions like Mg+2 or Fe+2 or  Gibbsite [Al(OH)3], if the cations are +3 like Al+3.  In the Brucite like structure (trioctahedral sheet silicate), all octahedral sites are occupied and in the Gibbsite like structure (dioctahedral sheet silicate) 2 out of 3 are occupied. T-O (1:1)- Repeating unit consist of one tetrahedral layer and one octahedral layer. Sandwich with spread and one bread T-O-T (2:1)- Repeating unit consist of one octahedral layer between two tethrahedral layers. Sandwich with spread between two bread T-O S Oxygen layer e Basal r p (O2-)+(OH-) e n Van der waals bonding OH- layer t i Apical n e T-O-T Basal (O2-)+(OH-) (O2-)+(OH-) Oxygen layer Van der waals bonding Apical  T-O and T-O-T both are soft-why?  Electrically neutral-bonding bet. repeat unit by van der walls and hydrogen bonding only.  Soapy feeling  T-O-T+C  C-interlayer cation  When Si+4 replaced by Al+3 in tetrahedral layer  K, Na in 12 fold co-ordination in the space between the repeat unit, i.e. 2 T- O-T layer T-O-T + C Al:Si=1:3 in mica  Electrically not neutral-bonding bet. repeat unit (i.e. Adjacent T-O-T layer) by van der walls and stronger ionic bonds involving interlayer cation. Harder compared to T-O and T-O-T. T-O-T - T-O-T layer bind to another T-O-T - T-O-T layer by weak Van der Waals bonds. It is along these layers of weak bonding that the prominent {001} cleavage  Brittle mica-replacement of Si+4 by Al+3 is more, Al+3 replaces 2 Si+4, imbalance of +2 charges, So, Ca+2 bet. Two T-O-T layer.  Because of the differences in charge balance between trioctahedral and dioctahedral sheet silicates, there is little solid solution between the two groups.  Within the trioctahedral sheet silicates there is complete substitution of Fe+2 for Mg+2 (Ex- Phlogopite-Annite).  Within the dioctahedral sheet silicates there is limited substitution of Fe+3 for Al+3 in octahedral sites.  F- or Cl- can substitute for (OH)- in the hydroxyl site.  T-O-T+O  O-octahedral layer Simplified Chlorite structure  Also called 2:1+1 layer (can have variable extent of substitution of Mg and Si by Al) T-O-T : Mg3Si4O10(OH)2 O : Mg3 (OH)6 Si substituted by Al in T-O-T layer : [Mg3Si3AlO10(OH)2]-1 Mg substituted by Al in octahedral layer : [Mg2Al (OH)6]+1 Chlorite: (Mg5Al)(Si3Al)O10(OH)8  Commonly, within T-O-T layer in Chl Al+3 substitutes Si+4 and gets –ve charge similar to micas.  In contrast to that the interlayer octahedral sheet has a net +ve charge after substitution of Al+3 by octahedrally coordinated divalent cations.  Results in stronger bonding between layers. Hardess of Chl 2-3 Serpentine T-O S Oxygen layer e Basal r p (O2-)+(OH-) e n Van der waals bonding OH- layer t i Apical n e  MgO:SiO2:H2O=3:2:2=1.5:1: Mg:Si:H = 3:2:4 Chemical Mg3Si2O5(OH)4 Formula: Composition: Molecular Weight = 277.11 gm Magnesium 26.31 % Mg 43.63 % MgO Silicon 20.27 % Si 43.36 % SiO2 Hydrogen 1.45 % H 13.00 % H2O Oxygen 51.96 % O  Rock types Protolith Elements Rocks Ultramafic rocks Very high Mg, Fe, Ni, Mantle rocks, and Cr. komatiites, and cumulates. Mafic rocks High Fe, Mg, and Ca. Basalts, gabbros, and some gray- wackes. Shales (or pelitic High Al, K, and Si. most common sedi rocks)- rock. Carbonates (or High Ca, Mg, and Mostly sedimentary calcareous rocks) CO2. limestones and dolostones. Impure Shale+carbonate may contain sand or carbonates components shale components. (marls) Iron Rocks Rich in Fe BIF, Iron stone  Requires Mg rich environment  Principally forms after hydrothermal alteration of UB (Dunite/peridotite)rocks.  Product of alteration of Olivine, Px  Cleavage: Distinct Color: Green, Red, Yellow, White. Density: 2.53 - 2.65, Average = 2.59 Diaphaneity Translucent to opaque : Fracture: Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz). Habit: Fibrous Luster: Resinous Streak: white serpentine.mp4 Talc T-O-T Basal (O2-)+(OH-) (O2-)+(OH-) Oxygen layer Van der waals bonding Apical  MgO:SiO2:H2O=3:4:1 Mg:Si:H = 3:4:2 Chemical Formula:18 Mg3Si4O10(OH)2 Composition: Molecular Weight = 379.27 gm Magnesium 19.23 % Mg 31.88 % MgO Silicon 29.62 % Si 63.37 % SiO2 Hydrogen 0.53 % H 4.75 % H2O Oxygen 50.62 % O ______ ______ 100.00 % 100.00 % = TOTAL OXIDE  Rock types Protolith Elements Rocks Ultramafic rocks Very high Mg, Fe, Ni, Mantle rocks, and Cr. komatiites, and cumulates. Mafic rocks High Fe, Mg, and Ca. Basalts, gabbros, and some gray- wackes. Shales (or pelitic High Al, K, and Si. most common sedi rocks)- rock. Carbonates (or High Ca, Mg, and Mostly sedimentary calcareous rocks) CO2. limestones and dolostones. Impure Shale+carbonate may contain sand or carbonates components shale components. (marls) Iron Rocks Rich in Fe BIF, Iron stone  Requires Mg rich environment  Low grade metamorphism of UB rocks  Metamorphism of impure CO3 (siliceous dolomitic rocks) Cleavage: Perfect Color: Pale green, White, Gray white, Yellowish white, Brownish white. Density: 2.75 Fracture: Uneven Habit: Foliated - Two dimensional platy forms. Hardness: 1 Luster: Vitreous - Pearly Streak: white Biotite T-O-T + C Al:Si=1:3 in mica Biotite K2O:MgO/FeO:Al2O3:SiO2:H2O=1:6:1:6:1 K:Mg/Fe:Al:Si:H=1:3:1:3:2 Chemical K(Mg,Fe++)3[AlSi3O10(OH,F)2 Formula: Composition: Molecular Weight = 433.53 gm Potassium 9.02 % K 10.86 % K2O Magnesium 14.02 % Mg 23.24 % MgO Aluminum 6.22 % Al 11.76 % Al2O3 Iron 6.44 % Fe 8.29 % FeO Silicon 19.44 % Si 41.58 % SiO2 Hydrogen 0.41 % H 3.64 % H2O Oxygen 43.36 % O Fluorine 1.10 % F 1.10 % F  Rock types Protolith Elements Rocks Ultramafic rocks Very high Mg, Fe, Ni, Mantle rocks, and Cr. komatiites, and cumulates. Mafic rocks High Fe, Mg, and Ca. Basalts, gabbros, and some gray- wackes. Shales (or pelitic High Al, K, and Si. most common sedi rocks)- rock. Carbonates (or High Ca, Mg, and Mostly sedimentary calcareous rocks) CO2. limestones and dolostones. Impure Shale+carbonate may contain sand or carbonates components shale components. (marls) Iron Rocks Rich in Fe BIF, Iron stone  Igneous-acidic rock (granite/ pegmatite). -intermediate compositon igneous rock. -Mg variety occur in K rich UB rock (Kimberlite) -In the acidic igneous rockFe component in biotite increases  Metamorphic- very common in metapelite forms under wide P-T range, other sedi rocks (siliceous lst/dol/metagreywacke)  Metagranite, metamorphosed K rich basic/UB rocks  Cleavage: Perfect  Color: Dark brown, Greenish brown, Blackish brown, Yellow, White.  Density: 3.09  Fracture: Uneven  Habit: Micaceous - Platy texture with "flexible" plates.  Hardness:2.5-3  Luster: Vitreous – Pearly  Streak: Gray biotite.mp4 Muscovite T-O-T + C Al:Si=1:3 in mica Muscovite K2O:Al2O3:SiO2:H2O=1:3:6:2 K:Al:Si:H=1:3:3:2 Chemical Formula: KAl2(Si3Al)O10(OH,F)2 Composition: Molecular Weight = 398.71 gm Potassium 9.81 % K 11.81 % K2O Aluminum 20.30 % Al 38.36 % Al2O3 Silicon 21.13 % Si 45.21 % SiO2 Hydrogen 0.46 % H 4.07 % H2O Oxygen 47.35 % O Fluorine 0.95 % F 0.95 % F  Rock types Protolith Elements Rocks Ultramafic rocks Very high Mg, Fe, Ni, Mantle rocks, and Cr. komatiites, and cumulates. Mafic rocks High Fe, Mg, and Ca. Basalts, gabbros, and some gray- wackes. Shales (or pelitic High Al, K, and Si. most common sedi rocks)- rock. Carbonates (or High Ca, Mg, and Mostly sedimentary calcareous rocks) CO2. limestones and dolostones. Impure Shale+carbonate may contain sand or carbonates components shale components. (marls) Iron Rocks Rich in Fe BIF, Iron stone  Cr Mus is named as Fuchsite  Li Mus as Lepidolite  Sericite is a fine grained white mica  Phengite generally has Si:Al>3:1, increase in Si is compensated by substitution of Al by Mg/Fe.  Igneous-Acid igneous rock (more common in aluminous one), less common that Bt  Sedimentary-Form mixed layer with clay mineral  Metamorphic-Most common in metapelite - Also found in other metasediments like marl, impure lst, greywacke -metamorphosed acidic rocks -In low grade environment formed by recrystallization of clay mineral (like Illite) Cleavage: Perfect Color: White, Gray, Silver white, Brownish white, Greenish white. Density: 2.82 Habit: Micaceous - Platy texture with "flexible" plates. Hardness: 2-2.5 Luster: Vitreous Streak: white muscovite.mp4 Chlorite T-O-T+O  MgO/FeO:Al2O3:SiO2:H2O=5:1:3:4 Mg/Fe:Al:Si:H=5:2:3:8 Chemical Formula: (Mg,Fe++)5Al(Si3Al)O10(OH)8 Composition: Molecular Weight = 595.22 gm Magnesium 15.31 % Mg 25.39 % MgO Aluminum 9.07 % Al 17.13 % Al2O3 Iron 11.73 % Fe 15.09 % FeO Silicon 14.16 % Si 30.28 % SiO2 Hydrogen 1.35 % H 12.11 % H2O Oxygen 48.38 % O  Rock types Protolith Elements Rocks Ultramafic rocks Very high Mg, Fe, Ni, Mantle rocks, and Cr. komatiites, and cumulates. Mafic rocks High Fe, Mg, and Ca. Basalts, gabbros, and some gray- wackes. Shales (or pelitic High Al, K, and Si. most common sedi rocks)- rock. Carbonates (or High Ca, Mg, and Mostly sedimentary calcareous rocks) CO2. limestones and dolostones. Impure Shale+carbonate may contain sand or carbonates components shale components. (marls) Iron Rocks Rich in Fe BIF, Iron stone  Hydrothermal alteration of Px, Amph, Bt in igneous rock  In sedi rock occur as detrital or authigenic xtal, occur in mix layered clay. Defines slaty cleavage in argillaceous sedi.  Metamorphic rock-common in low grade metamorphic facies (zeolite facies, prehnite-pumpellyite facies) In metapelite (Chl zone) In metabasic rocks (greenschist) Cleavage: Perfect Color: Blackish green, Bluish green, White, Yellowish green, Olive green. Density: 2.55 - 2.75, Average = 2.65 Fracture: Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern. Habit: Fibrous Hardness: 2-2.5 Luster: Vitreous - Pearly Streak: white chlorite.mp4 Clay minerals  Phyllosilicates can also occur as clay mineral, compositionally hydrous aluminosilicates  Crystal sizes less than 2 m in diameter.  Clay mineral can exchange cations with an aqueous phase. This is an important property that can have a significant impact on the distribution of metals in the environment.  CEC (Cation Exchange Capacity) determined by measuring the uptake and release of NH4+ from a 1M ammonium acetate solution at pH=7  CEC varies as a function of pH, size, ions, surface charge  Surface charge arises in clay mineral due to 3 causes- i) Substitution in tetrahedral and Octahedral layers ii) Defects or imperfections in the crystal structure (missing cations) iii) Unsatisfied or broken bonds at the edges or corners Geology of Clay mineral  Forms as a result of interaction of silicate rock and water in low temp. Interaction. Common example Kaolinitization of K- feldspar (Hydrolysis)  Clays are formed near earth surface as a result of weathering, soil formation, sediment transport and deposition, compaction, diagenesis. Also by hydrothermal alteration.  Therefore abundant in weathered rock, soil, fine-grained clastic sedi, hydrothermally altered rocks.  Composition of clay mineral depend on parent rock. Also on temp., H2O composition/avaiibility and time.  Intense weathering in wet climate tend to favour kaolinite whereas dry temperate climate favour smectite  Polytypism is a type of polymorphism wherein different polymorphs exist in different domains of the same crystal. It has to do with the way that individual layers are stacked within a crystal structure.  Mixed-layer clay minerals are materials in which different kinds of clay layers alternate with each other.  The mixing or interstratification in vertical stacking can be regular (ordered), segregated regular, or random  Commonly described mixed-layer clays include: illite-vermiculite, illite-smectite, chlorite-vermiculite, chlorite-smectite, and kaolinite-smectite. Common Sheet silicates – like clay minerals Orthorhombi Orthorhombic, Monoclinic, c, single two stacking single stacking vectors, not stacking vector, 90º 90º vector, not 90º Fig. 4-14 T-O Oxygen layer Basal (O2-)+(OH-) Van der waals bonding OH- layer Apical  Limited substitution in the structure. So CEC is very low.  Structural units attached to each other by weak Van der Walls bonds, soft mineral-soft clay and easily deformable.  Kaolinite does not contain much interlayer cations and water.  They are not easily expandable Illite T-O-T+C (K as interlayer ion)  Illite Similar structure to Muscovite, Illite has fewer interlayer cation in comparison to Mus leading to weaker bonding and less regularity in stacking of Illite sheets Low CEC, low expandibility Smectite/Montmorillonite T-O-T/T-O-T+C Smectite (structure like talc/pyrophyllite Montmorillonite (smectite with interlayer Ca, Na) Basal (O2-)+(OH-) (O2-)+(OH-) Oxygen layer Van der waals bonding Apical  In Smectite basal spacing can expand.  Number of substitutions are possible (Fe, Mg substituting Al and Al substituting Si) and is balanced by cations in interlayer position  CEC is high  Depending on the composition the expandibility of the mineral varies. Clay mineral will expand as the water content of the immediate environment increases. Vermiculite T-O-T + C  Trioctahedral with Mg interlayer cation Mg  Interlayer space is not much expandable because of stronger electrostatic force holding the sheets.  They have similar CEC like smectite. Chlorite T-O-T+O Mixed layer clay Metamorphism of clay mineral  Clay mineral sediments are generally smectite rich.  With burial, recrystallization of clay mineral takes place. Ex- Smectite into Illite during diagenesis The extent of conversion depend on availibility of K.  Amount of Chl increases with increase in depth, decrease in kaolinite  Above ~200oC clay minerals get converted by metamorphic processes into coarse grained Chl, Micas and other minerals. Effect on environment  Effect on plant-ability of absorb/adsorb, release various molecules (H2O, N2) which plant can use.  Can pose substantial engineering problem. Clay mineral can shrink during dry periods and can swell during wet periods. This can cause problem to foundation of buildings, roads etc.  Sediment containing volcanic ash deposited in marine conditions. They may alter to clay rich in smectite and can have high potential for shrinking and swelling.  ‘Bentonite’ is aplied to rocks containing abundant sweling problems and tends to be more susceptible to slope stability problems. Relict altered ash beds are referred as bentonite beds. Uses of Clay  Paper coating and filler  Drilling and additive  Ceramics  Filler-Used in rubber, plastics, paint etc.  Cosmetics- Both as filler and colorant  Refractory products-fire brick  Building products-bricks  Portland cement  Pharmaceuticles-Active ingredient as an inert filler (Kaolinite)  Absorbents  absorb oil and other chemical in industrial setting for remediation and protection  For environmental protection like installing clay layer beneath waste dump or contaminated pond to prevent migration of contaminated water into the ground water supply.