UNIVERSITY OF SOUTH ALABAMA GY 302: Crystallography & Mineralogy Lecture 24: Phyllosilicates 2 Serpentine and Clays Last Time Phyllosilicates 1 General chemistry/structure Phyllosilicate classification Mica, chlorite and talc groups Phyllosilicate Minerals (excludes clays, serpentine groups, and others) Phyllosilicate Structure Phyllosilicate Structure (Mica) 4- Si4O10 cross sectional view Phyllosilicate Classification 2:1 Structure (Most micas and clays) 1:1 & 2:1 Interlayered (Chlorite Group) 1:1 Structure (kaolinite, serpentine halloysite, Chrysotile, allophane) Phyllosilicate Structure C-axis Perfect Basal Cleavage Today’s Agenda Phyllosilicates 2 1. Serpentine Group 2. Other Phyllosilicates 3. Clay Minerals (Chemistry, modes of analysis) More Phyllosilicate Minerals Mineral Formula System “Clay” Minerals Kaolinite Al2Si2O5(OH)4 Triclinic ”Smectite” (Na,Ca)0-3(Al,Mg)2Si4O10(OH)2·n(H2O) Monoclinic *Bentonite (Na,Ca)0-3(Al,Mg)2Si4O10(OH)2·n(H2O) Monoclinic Illite (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2·(H2O) Monoclinic Serpentine Group (17 minerals) ”Serpentine” (Mg, Fe, Ni)3Si2O5(OH)4 Monoclinic Antigorite Mg3Si2O5(OH)4 Monoclinic Chrysotile Mg3Si2O5(OH)4 Monoclinic Other Phyllosilicates Stilpnomelane (series) ~K(Fe, Al)10Si12O30(OH)2 Triclinic Prehnite (series) Ca2Al(AlSi3O10)(OH)2 Orthorhombic Sepiolite Mg4Si6O15(OH)2·6(H2O) Orthorhombic Garnierite (Ni,Mg)4Si6O15(OH)2·6(H2O) Orthorhombic Apophylite KCa4(Si4O10)2F·8(H2O) Tetragonal ++ *Astrophyllite** K2Na(Fe ,Mn)7Ti2Si8O26(OH)4 Triclinic Phyllosilicates Si:O ratio = 2:5 (3 shared oxygens) -4 -8 Anion component: Si4O10 or Si8O20 -5 -6 With Al substitution: AlSi3O10 or Al2Si2O10 General Formula: XYAlSi3O10(OH)2 X = K+, Na+, Li+, Ca2+ Y = Fe2+/3+, Mg2+, Al3+, rarely Cr3+, Ni3+, Mn3+ Example (“Smectite”): (Na,Ca)0-3(Al,Mg)2Si4O10(OH)2·n(H2O) Phyllosilicate Structure Tetrahedral layers 4- (mostly SiO4 ) Cation layers (K+, Mg2+, Na+ etc.) also H2O (clays) Octahedral layers (variable; Al/Mg/OH) Phyllosilicate Structure The octahedral layers are given specific names according to the nature of the “filling”. Need 6 x OH for octahedral coordination Phyllosilicate Structure The octahedral layers are given specific names according to the nature of the “filling”. Need 6 x OH for octahedral coordination Al2(OH)6 = Gibbsite Layer (Al(OH)3) 2 x Al = dioctahedral coordination Mg3(OH)6 = Brucite Layer (Mg(OH)2) 3 x Mg = trioctahedral coordination Phyllosilicate Classification Is rather nasty, but most are either monoclinic or triclinic. Classification is further done of the basis of: 1. composition of octahedral layer 2. repeat distance (distance between T-O-T “sandwiches”) 3.Whether structure is expandable (clays) 4. Number of layers in the “sandwiches” (2 versus 3) Phyllosilicate Minerals (Serpentine Group) Phyllosilicate Minerals (Serpentine Group) “Serpentine” (antigorite) [(Mg, Fe, Ni)3Si2O5(OH)4 ] Crystal: Monoclinic Pt. Group: m Habit: Acicular (“fibrous”) SG: 2.5 to 2.6; H: 3.5 to 4 L: silky, greasy, waxy; Str: green- white Col: white, yellow, green to black Clev: good [001] http://webmineral.com/specimens/picshow.php?id=1377 Optics: Biaxial (-); bir=0.005-0.006 Named because of its resemblance to snake skin nα=1.555; nβ=1.56, nγ=1.56 Occurrence: alteration of ultramafic minerals Phyllosilicate Minerals (Serpentine Group) Chrysotile (Incl. clinochrysotile and orthochrysotile) [Mg3Si2O5(OH)4] Crystal: Monoclinic Pt. Group: 2/m Habit: Acicular (“fibrous”) SG: 2.53; H: 2.5 L: silky; Str: grey Col: green Clev: good [110], [010] http://webmineral.com/specimens/picshow.php?id=1377 Optics: Biaxial (?); bir=0.010 Named from the Greek chrysos - "gold" and tilos - "fiber." nα=1.569; nβ=?, nγ=1.57 Occurrence: metamorphic rocks (Quebec, Canada) Phyllosilicate Minerals (Serpentine Group) “Tiger’s Eye” [Mg3Si2O5(OH)4] Crystal: N/A Pt. Group: N/A Habit: Acicular (“fibrous”) SG: 2.65; H: 7 L: silky; Str: N/A Optics: N/A http://www.twistedtree.org.uk/Tigers_Eye_2.JPG Col: yellow gold to red Clev: N/A Ino-Phyllosilicate “Hybrids*” Prehnite [Ca2Al(AlSi3O10)(OH)2] Crystal: Orthorhombic Pt. Group: 2mm (or mm2) Habit: globular, stalactitic SG: 2.87; H: 6 to 6.5 L: vitreous, waxy, pearly; Str: white http://webmineral.com/specimens/picshow.php?id=1377 Col: colourless (yellowish, greenish) Clev: good [001] Named after Dutch Colonel, H. Von Prehn Optics: Biaxial (+); bir=0.022-0.033 (1733-1785). nα=1.61; nβ=1.615, nγ=1.632 Occurrence: hydrothermal * A mixed inosilicate-phyllosilicate mineral Ino-Phyllosilicate “Hybrids*” Okenite [Ca3Si6O15)•6H2O] Crystal: Triclinic Pt. Group: 1 Habit: fibrous (spherical aggregates) SG: 2.31; H: 5 L: pearly; Str: white Col: white (yellowish, bluish) Clev: good [001] http://webmineral.com Optics: Biaxial (-); bir=0.003-0.010 Named for Lorenz Oken(1779-1851). nα=1.512; nβ=1.514, nγ=1.515 Occurrence: secondary alteration of basalt * A mixed inosilicate-phyllosilicate mineral Ino-Phyllosilicate “Hybrids*” Astrophyllite Group ++ K2Na(Fe ,Mn)7Ti2Si8O26(OH)4 Crystal: Triclinic Pt. Group: 1 Habit: bladed (radiating) SG: 3.34; H: 3 to 3.5 L: vitreous, pearly; Str: yellowish-brown Col: brown-bronze (yellow-green) Clev: perfect [001] Optics: Biaxial (+); bir=0.050 http://webmineral.com/specimens/picshow.php?id=1377 nα=1.680; nβ=1.700, nγ=1.730 * A mixed inosilicate-phyllosilicate mineral Occurrence: igenous syenites From the Greek aster - "star" and fyllon - "leaf." (zircon-bearing) Phyllosilicate Minerals (“Clay” Group) Kaolinite [Al2Si2O5(OH)4 ] Crystal: Triclinic Pt. Group: 1 Habit: platy (microscopic) SG: 2.6; H: 1.5 to 2 L: earthy; Str: white Col: white (variable shades) Clev: perfect [001] Optics: Biaxial (-); bir=0.007 Named after Kao-Ling, China in reference to porcelain pottery nα=1.553; nβ=1.559, nγ=1.56 Occurrence: sedimentary alteration Phyllosilicate Minerals (“Clay” Group) Kaolinite SEM image [Al2Si2O5(OH)4 ] Crystal: Triclinic Pt. Group: 1 Habit: platy (microscopic) SG: 2.6; H: 1.5 to 2 L: earthy; Str: white Col: white (variable shades) Clev: perfect [001] Optics: Biaxial (-); bir=0.007 nα=1.553; nβ=1.559, nγ=1.56 Occurrence: sedimentary alteration Phyllosilicate Minerals (“Clay” Group) Illite SEM image (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2·(H2O) Crystal: Monoclinic Pt. Group: 2/m Habit: wispy (microscopic) SG: 2.75; H: 1 to 2 L: earthy; Str: white Col: white (variable shades) Named in 1937 for the Clev: perfect [001] state of Illinois where the mineral was first Optics: Biaxial (-); bir=0.030-035 described. nα=1.535; nβ=1.555, nγ=1.565 Occurrence: sedimentary (marine) alteration Phyllosilicate Minerals (“Clay” Group) Smectite (Montmorillonite) SEM image [(Na,Ca)0-3(Al,Mg)2Si4O10(OH)2·n(H2O) ] Crystal: Monoclinic Pt. Group: 2/m Habit: platy (microscopic) SG: 2.35; H: 1.5 to 2 L: earthy; Str: white white (variable) Col: Named after Veinne, Clev: perfect [001] Montmorillone, France Optics: Biaxial (-); bir=0.015-0.020 nα=1.485; nβ=1.504, nγ=1.505 Occurrence: sedimentary Phyllosilicate Minerals (chlorite group) Chlorite (Chlinochore) SEM image (Mg,Fe)3(Al,Si)4O10(OH)2(Mg,Fe)3(OH)6 Crystal: Monoclinic Pt. Group: 2/m Habit: scaly, platy (microscopic) SG: 2.65; H: 2 to 2.5 L: vitreous/pearly; Str: white Col: green to black From the Greek klino - "oblique" and chloros - Clev: perfect [001] "green” Optics: Biaxial (-); bir=0.005-0.011 nα=1.571; nβ=1.571, nγ=1.576 Occurrence: low grade-metamorphism, epithermal diagenesis Phyllosilicate Minerals Diatomite SiO2 (rock, not mineral) Crystal: N/A Pt. Group: N/A Habit: N/A SG: 0.2-0.3!; H: 1 L: earthy; Str: white Col: white, cream Clev: N/A Optics: N/A Occurrence: sedimentary Name Derivation: From its diatom content Phyllosilicate Geochemistry 2:1 Structure (Most micas and clays) 1:1 & 2:1 Interlayered (Chlorite Group) 1:1 Structure (kaolinite, serpentine halloysite, Chrysotile, allophane) Clay Geochemistry (1:1 structure) Halloysite (Expandable) + K H2O kaolinite (Non-expandable) Clay Geochemistry (1:1 structure) Halloysite (Expandable) 70nm 100 nm + K H2O kaolinite (Non-expandable) Clay Geochemistry (1:1 structure) Halloysite (Expandable) 70nm “glycol” K+ kaolinite (Non-expandable) Clay Geochemistry (2:1 structure) Smectite (Expandable) + K H2O Illite/Muscovite (Non-expandable) Clay Geochemistry (2:1 structure) Smectite (Expandable) 100 nm 170 nm K+ “glycol” Illite/Muscovite (Non-expandable) Clay Mineral Analysis Clay Mineral Analysis Is primarily done using XRD (X-ray diffraction). In order to understand how this works, you need to consider physics (yuck). All images in the latter part of this lecture, unless otherwise stated, are stolen from: http://pubs.usgs.gov/of/2001/of01-041/htmldocs/clays/kaogr.htm Clay Mineral Analysis Clay Mineral Analysis Clay Mineral Analysis Is primarily done using XRD (X-ray diffraction). In order to understand how this works, you need to consider physics (yuck). Clay Mineral Analysis Is primarily done using XRD (X-ray diffraction). In order to understand how this works, you need to consider physics (yuck). Clay Mineral Analysis Clay Mineral Analysis Clay Mineral Analysis Clay Mineral Analysis CHLORITE Today’s Stuff To Do 1. Posters in for printing: One Week Today - 5:00 PM 2. Inosilicates minerals quiz 12:15-12:45 PM 3. No online lecture this week Next Time 1. No Lecture…… 2. Final exam 100 mineral list next Thursday GY 302: Crystallography and Mineralogy Lecture 24: Silicates 7: Clays and XRD Instructor: Dr. Doug Haywick [email protected] This is a free open access lecture, but not for commercial purposes. For personal use only. .