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Clay Mineral XRD Sample Preparation and Interpretation
Connie Constan, guest lecture
EPS 400, 04/04/2012
Ceramic XRD patterns
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 – Supplies and equipment
available
– Purpose of analysis
– Material itself
– Your knowledge and ingenuity
USGS Open-File Report 01-041
USGS Open-File Report 01-041
Disaggregate the Rock
Utrasonic Probe Mortar and Pestle
Waring Laboratory Blender McCrone Micronising Mill
Chemical Pretreatments
• Removal of carbonates – Acetic acid
• Removal of organics – Hydrogen peroxide
• Removal of sulfates
• Removal of iron oxides
• Cation saturation
USGS Open-File Report 01-041
These acids can cause burns. Wear goggles, plastic gloves, and an apron while working with these chemicals.
Particle Size Separation
• Methods – Decantation
– Centrifugation
• Settling times – Stoke’s Law
• Dispersant/deflocculant – sodium
hexametaphosphate
USGS Open-File Report 01-041
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 – All
• Level of skill needed – Low
• Application – Qualitative analysis
Moore and Reynolds Figure 6.1
USGS Open-File Report 01-041
Smear Mount
• Advantage – Quick, moderately
homogenous
• Disadvantage – Most
• Level of skill needed – Moderate
• Application – Clay and nonclay
minerals USGS Open-File Report 01-041
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
• Level of skill needed – High
• Application – Crystal structure studies
Moore and Reynolds Figure 6.4
Porous Ceramics www.sentrotech.com
Ethylene Glycol Solvation
Images from USGS Open-File Report 01-041
Random Mount
• Why?
USGS Open-File Report 01-041 Moore and Reynolds Figure 6.5
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
• Automated diffraction mapping in Rapid II system
CBO-f Polycap
CBO Parabolic
General Principles of Identification
• Basal (00l) spacing
Calculated X-ray diffraction pattern of antigorite www.gly.uga.edu/Schroeder/geol6550/CM07.html
Illite Diffractogram www.gly.uga.edu/schroeder/geol6550/CM11.htm
Illite and Glauconite
Moore and Reynolds Figure 7.3
Glauconite-rich sandstone
Chlorite and Kaolinite
Moore and Reynolds Figure 7.4
USGS Open-File Report 01-041
Smectite
Moore and Reynolds Figure 7.8
USGS Open-File Report 01-041
Vermiculite
Moore and Reynolds Figure 7.7
USGS Open-File Report 01-041
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 odd-
numbered 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
yTwo methods
Índice de KublerFWHM
FWHM8 9 10
°2Θ
FWHM = full width athalf maximum
Índice de Eberl y Velde
Smectite-rich I/S
Well-crystallized illite (WCI)Poorly-crystallized illite (PCI)
Illite-rich I/S
4 6 8°2θ, CuKα
Gharrabi et al., 1998 CCM, 46:79-88
Righi and Elsass, 1996 CCM, 44:791-800Peak Decomposition
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
Qal Fm. Ceramic
My Results
Gallina Black-on-gray ceramic sherd
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.