clay mineral xrd sample preparation and interpretation - eps homepage

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


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


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



Oriented Methods

• Why?


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


Smear Mount

• Advantage – Quick, moderately

homogenous

• Disadvantage – Most

• 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

• 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?

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


Glauconite-rich sandstone

Chlorite and Kaolinite



Smectite



Vermiculite



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.

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