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Clay Mineral XRD Sample Preparation and Interpretation
Clay Mineral XRD Sample Preparation and Interpretation Ceramic XRD patterns Connie Constan, guest lecture EPS 400, 04/04/2012 What are clays? • Fine-grained • Earthy • Plastic when moist • Group of minerals • Category of rocks and soils • Particle-size grade (<2µm) Phyllosilicates • • • • kaolin group (two-layer clays) smectite group (three-layer, expanding lattice) illite group (three-layer, non-expanding) chlorite group (three-layer with interlayer cations) Images from Railsback's Some Fundamentals of Mineralogy and Geochemistry Hydrous-Magnesian Clays • Lath structure clays • Chain-like arrangement • palygorskite group • sepiolite group Sepiolite/Meerschaum pipe bowls Sample Preparation • Constraints USGS Open-File Report 01-041 USGS Open-File Report 01-041 – Supplies and equipment available – Purpose of analysis – Material itself – Your knowledge and ingenuity Disaggregate the Rock Mortar and Pestle Waring Laboratory Blender Utrasonic Probe McCrone Micronising Mill Chemical Pretreatments • Removal of carbonates – Acetic acid • Removal of organics These acids can cause burns. Wear goggles, plastic gloves, and an apron while working with these chemicals. – Hydrogen peroxide • Removal of sulfates • Removal of iron oxides • Cation saturation USGS Open-File Report 01-041 Particle Size Separation • Methods – Decantation – Centrifugation • Settling times USGS Open-File Report 01-041 – Stoke’s Law • Dispersant/deflocculant – sodium hexametaphosphate USGS Open-File Report 01-041 Oriented Methods • Why? USGS Open-File Report 01-041 Velde and Druc 1999: Figure 3.8 Glass Slide • Advantage – Quick • Disadvantage Moore and Reynolds Figure 6.1 – All • Level of skill needed – Low • Application – Qualitative analysis USGS Open-File Report 01-041 Smear Mount • Advantage – Quick, moderately homogenous • Disadvantage – Most USGS Open-File Report 01-041 • Level of skill needed – Moderate • Application – Clay and nonclay minerals USGS Open-File Report 01-041 Filter Transfer • Advantage – Homogenous aggregate • Disadvantage – Fair intensities • Level of skill needed – Moderate • Application – Quantitative representation Images from USGS Open-File Report 01-041 Porous Plate • Advantage – Best intensities • Disadvantage – Inhomogeneous aggregate Moore and Reynolds Figure 6.4 • Level of skill needed – High • Application – Crystal structure studies Porous Ceramics www.sentrotech.com Ethylene Glycol Solvation Images from USGS Open-File Report 01-041 Random Mount • Why? Moore and Reynolds Figure 6.5 USGS Open-File Report 01-041 New Instrumentation! • Rigaku SmartLab – – – – Nanomaterials Thin films Powder & bulk Metals & alloys • Rigaku Rapid II – – – – Mounted samples Thin films Capillaries 2D detector/image plate Microdiffraction • Point Focus geometry in SmartLab system CBO Parabolic CBO-f Polycap • Automated diffraction mapping in Rapid II system General Principles of Identification • Basal (00l) spacing Illite Diffractogram Calculated X-ray diffraction pattern of antigorite www.gly.uga.edu/schroeder/geol6550/CM11.htm www.gly.uga.edu/Schroeder/geol6550/CM07.html Illite and Glauconite Glauconite-rich sandstone Moore and Reynolds Figure 7.3 Chlorite and Kaolinite USGS Open-File Report 01-041 Moore and Reynolds Figure 7.4 Smectite USGS Open-File Report 01-041 Moore and Reynolds Figure 7.8 Vermiculite USGS Open-File Report 01-041 Moore and Reynolds Figure 7.7 Sepiolite, Palygorskite, Halloysite • Sepiolite 6.9 deg 2θ • Palygorskite 8.5 deg 2θ • Halloysite ~20 deg 2θ Scanning electron image of halloysite www.gly.uga.edu/Schroeder/geol6550/halloysite.gif Polytypes • 1M and 2M1 most common polytypes – Use diagnostic hkl reflections tables in Moore and Reynolds (Tables 7.5 to 7.7) • Turbostratic Stacking – Wide band at hk (13,20) asymmetiric towards wide angles in XRD Figures from Meunier (2005: Figure 1.12) Mixed-Layered Clays • Illite/Smectite (I/S) – Ethylene glycol solvation – Reichweite ordering between 5 and 8.5 degrees 2θ – Percent illite estimation from value of Δ2θ • Chlorite/Smectite (C/S) – Expansion with ethylene glycol solvation – Expansion with Mg saturation and glycerol solvation Mixed-Layered Clays • Chlorite/Vermiculite – – – – – – Ethylene glycol solvation Mg saturation Glycerol solvation Heat treatment Air-dried condition Percent from Δ2θ • Kaolinite/Smectite – Ethylene glycol solvation – Heat treatment – Percent from Δ2θ • Serpentine/Chlorite – Broadening of oddnumbered peaks – Equation to determine percent serpentine • Mica/Vermiculite – – – – Heat treatment Mg saturation Glycerol solvation Use low-angle reflection (001/001) for percent and Reichweite ordering Non-Clay Minerals MINERAL TYPE SHOWN D SPACING ANGLE 2θ Silicas α quartz 4.27, 3.342 20.8, 26.67 Feldspars K-spar, Plag 3.19, 3.24 27.95, 27.52 Zeolites solid solution series Approx. 8-9 <12 Carbonates Calcite, Dolomite 3.04, 2.89 29.43, 30.98 Sulfates Gypsum, Anhydrite 7.61, 3.50 11.7, 25.46 Quantitative Analysis • Required Sample Characteristics – – – – Length Thickness Position Homogeneity Figures from Moore and Reynolds (1997) Quantitative Analysis • Mineral Reference Intensities • Peak Intensity Measurement • Peak Decomposition Smectite-rich I/S Well-crystallized illite (WCI) Poorly-crystallized illite (PCI) y Two methods FWHM Illite-rich I/S 4 Índice de Ku bler 6 °2θ, CuKα Peak Decomposition FWHM 8 9 °2Θ 10 Índice de Eberl y Velde FWHM = full width at half maximum 8 Gharrabi et al., 1998 CCM, 46:79-88 Righi and Elsass, 1996 CCM, 44:791-800 Clay Quantification • The best diffraction peaks to use are as close together as possible • Avoid the low diffraction angle region • Do not use external standards • Need random orientation when both clay and non-clay minerals are present in a single sample • Use integrated intensities and calculated calibration factors Clay Quantification QUANTITATIVE X-RAY DIFFRACTION ANALYSIS OF CLAY-BEARING ROCKS FROM RANDOM PREPARATIONS Srodon et al 2001 Clays and Clay Minerals 49(6):514–528 My Research • What clay minerals were available locally? • What clay minerals were used in Gallina ceramics? Natural Clays Geology = seven formations Ceramics Archaeology = three types My Results Gallina Black-on-gray ceramic sherd Ceramic Qal Fm. Estimated Original Firing Temperature Clay pattern at each temperature: unfired, 300, 600, 750, and 900ºC Summary • “Identifying clay minerals for their diffraction tracing is something of a Gestalt process, i.e., identifying the whole – being able to say that it is an illite/smectite because it has an illite/smectite pattern.” (Moore and Reynolds 1997:296) • In other words, you just have to learn what the characteristic patterns look like for each clay mineral and the mixed-layered clays.
