Transmission Electron Microscopy of
Mineralogy
Wen-An Chiou
Materials Characterization Center (MC2)
and
Department of Chemical Engineering and Materials Science
University of California, Irvine
Irvine, CA 92697-2575
USA
Pan-American Advanced Studies Institute on
Transmission Electron Microscopy in Materials Science
July 11, 2006
Beginning with a cloud of dust and gas
from which the solar system formed some 5 billion years ago, to
the birth of the Earth about 4.7 billions years ago. The earth is a
very special place – and not just because we humans inhabit it.
.
To the planet we know today, with its hospitable atmosphere
and rich resources, a planet still active inside – as evidenced
by earthquakes, volcanoes, ocean basins that open and close,
and continents that drift apart.
Geology – We explore not only the Earth as it exists today; we
also seek answers how it was formed, what it was like when
first born, to understand the Earth, both present and the past.
From the Small World to the Huge Earth and the
Universe
PURPOSES
(1) To give a general overview/review of the
application of TEM in the mineralogical and
geological sciences research.
(2) To show examples of mineralogical and
geological researches that have been utilizing
TEM.
(3) To stimulate, hopefully, the direction of future
mineralogical and geological research in the
application of TEM.
The Rock Record
• The only record we have of things that happened on Earth in the
geological past is the rock.
• What is a rock? A rock is many things. It is a collection of the
particular chemical elements that make it up.
• Physical and chemical characteristics of minerals in the rocks – most
tangible link with the history of the Earth. The logical beginning of the
science of geology.
• Minerals are also important in practical way. Civilization history and
technological culture are related to minerals and rocks.
Brief History of Mineralogical/Geological Research
Related to Microscopy
• 1851, Henry Clifton Sorby, developed a technique of preparing rock thin
section (25 um thick), and examined with an optical microscope.
• 1912, von Laue, diffraction of X-ray by crystal, and W. L. Bragg Law of
crystal diffraction, from which the actual positions of atoms in a crystal
can be determined.
• For many years, polarized LM and XRD have been the major techniques
for study of minerals.
• In the past a few decades, many techniques used for investigating the
structure and properties of materials have been utilized in mineralogical
research.
• In the past two decades, growing awareness that the study of mineral
behavior has important implications in related disciplines in earth
sciences, even to the level where continental-scale tectonic phenomena
are being considered in terms of processes taking place within individual
mineral grains.
• Fleet and Ribbe (1961) - Probably the first significant application of
TEM to an important rock-forming mineral (found submicroscopic
microstructure of alternating lamellae of orthoclase which provide a
detailed explanation of complex diffraction pattern)
• Early 1960s, other feldspars were studied by the Cambridge group, and
also by Nissen and by McLaren group.
• McLaren and phakey (1965), first series of papers on variety of quartz
(found dislocations in milky vein quartz and determined Brazil and
Dauphine twin boundaries)
• However, little work was done at the time on these nonmetallic materials
compared with the very great use that was made on TEM in metallurgy.
The main reason was the difficulty of preparing thin enough samples
• Development of ion beam thinning technique has the similar impact like
that Sorby’s until early 1970s, these serious limitations were largely
overcome by ion beam thinning technique (originated by Paulus and
Reverchon in 1961).
• Wenk (1976) edited the book “Electron Microscopy in Mineralogy”,
TEM had changed the aspect of mineralogy.
• TEM-as an instrument for high resolution imaging,
electron diffraction, and chemical analysis has produced a
major impact in mineralogical/geological studies in a
relative short time despite the late take off of TEM
application in mineralogy (as compared with materials
science and biological/medical sciences).
• Imaging
Diffraction
Analytical tech. Of TEM
• Optical M
XRD
Geochemical Method
• It is not exaggerate to say:
The study of minerals has been among the most important
contribution of HRTEM (because many minerals, unlike
metals or other simple structures, have relative large unit
cell and large scale defects that can be imaged successfully
with TEM).
• The most important pieces of information required to
characterize a mineral are:
– (1) Crystal structure
– (2) Chemical composition
• TEM is capable to obtain both structure and chemical
information from a small area down to 1 nm (in diameter).
• No other technique can provide imaging (both
texture/fabric and internal structure), crystallographic
information (electron diffraction), and chemical
composition simultaneously from a very small region (1
nm).
• TEM is a logical complement and extension of some of the
more established mineralogical techniques and instruments.
Geomaterials vs. Man-made Materials
• The goal of mineralogical research coincide with those for many
other materials research.
• Minerals (geomaterials)
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Materials Science
God’s Materials
Man-made materials
Unknown
Known composition
Complex
Simpler
All crystallographic systems Most cubic, tetragonal, hexagonal
Recorder of geological processes and events
Important tool for reconstructing the past
• TEM has had its great mineralogical impact in the study of
localized structure and chemical perturbations in minerals.
– E.g., Crystal defects, twinning, exsolution lamellae,
intergrowth
– All contain much information regarding the history of a
mineral, thus of geological interest.
Relationship both within and between grains of a rock
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Grain boundary
The geometry of fine-grained mineral intergrowth
The interfaces
Minerals inclusions and precipitates
Compositional zoning
Pure crystallography
Structural and chemical disorder
Nonstoichiometry
Reaction mechanisms
Polymorphic and polytypic transformations
Major Research Groups (I)
• Hard Rock:
– Wenk, H.-R., (UC, Berkeley), 1976, ed., Electron Microscopy in
Mineralogy, Springer-Verlag, This book changed the aspect of
mineralogy.
– Buseck, P. R., (ASU), 1988, co-ed., High-Resolution
Transmission Electron Microscopy and Associated Techniques,
Oxford U Press
– Banfield, J. F., (UC, Berkeley)
– Veblen, D. R. (John Hopkins)
– Mclaren A. C. (Australian National Univ.), 1991, Transmission
Electron Microscopy of Minerals and Rocks, Cambridge Univ.
Press
– Ewing, R. (U of Michigan), emphasis on radiation damage on
rocks
– American Mineralogists (Journal by the Mineralogical Society of
America)
– Others
Major Research Groups (II)
• Soft Rock:
• 1967, Zvyagin, Boris B., (translated by Simon Lyse), ElectronDiffraction Analysis of Clay Mineral Structures, Plenum Press.
• The geometry theory of electron diffraction and analysis of clay
mineral diffraction patterns. The determination of intensities in
layer silicate diffraction patterns.Experimental electron
diffraction studies of clays and related minerals.
• 1968, Beutelspacher, H. and H. W. Van Marel, Atlas of Electron
Microscopy of Clay Minerals and their Admixtures, A Picture
Atlas, Elsvier Publishing Co.
• A very comprehensive electron microscopy survey of
morphology from a variety of clay and associated minerals.
• 1971, Gard, J. A. (ed.), The Electron-Optical Investigation of
Clays, Mineralogical Society (Clay Minerals Group). A
thorough study of the crystallography and morphology of a
variety of clay and related minerals using transmission electron
microscopy.
• 1990, Mackinnon, I. D. R. and F. A. Mumpton, ElectronOptical Methods in Clay Science, The Clay Minerals Society.
• Clay mineralogy studies:
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Veblen, D. R. group
Peacor, D. group (Univ. of Michigan)
University of Tokyo (Japan) group
European research groups
Clay and Clay Minerals, by the Clay Minerals Society.
Others
• 1986, Bennett, R. H. and M. H. Hulbert, Clay Microstructure,
International Human Resources Development Corp.
• 1991, Bennett, R. H., W. R. Bryant and M. H. Hulbert, Microstructure
of Fine-Grained Sediments, From Mud to Shale, Springer-Verlag.
• Clay fabric studies – geotechnical properties using TEM
– Texas A&M group
– Naval Research Laboratories
– Civil Engineering groups
Application of TEM in Earth Sciences
• (1) in mineralogical and geological sciences
– This presentation
– (a) Conventional TEM – Minerals ID
- Defect and microstructure
– (b) HRTEM – Determination of the atomic structure
Perfect and defected minerals/crystals
• (2) in clay science and civil engineering
– Thursday (July 13th) presentation
• (3) in biominerals and biomineralization
– Tuesday (July 18th) presentation
• (4) in-situ environmental TEM research
– Friday (July 20th) presentation
Mineralogical Applications (1) - Conventional TEM
• Mineral Identification
– Morphological
– Only on some very typical minerals such as some clay
minerals
– Kaolinite:
Hexagonal
– Attapulgite:
Needle
(Both images from Beutelspacher, H. and H. W. Van Marel, 1968)
• Mineral identification
– Electron diffraction:
Positive ID, assisted with chemical analysis (EDS)
(From Zvyagin, 1967)
Mineral Identification
Electron diffraction: Shape factor and crystal morphology
(From Gard, 1971)
• Defect and Microstructure
– 1950s Metallurgists studies the
dislocation in the plastic deformation
of crystalline materials.
– 1960s, The mechanism of dislocation
movement have established.
– At low temperature dislocations
move “conservatively” on slip planes,
requiring only small shearing
stresses. Their density increases and
due to increasing forces the strain
energy of the deformed crystals
augments.
– Example: High dislocation density in
a low carbon steel (typical structure
of materials deformed plastically at
low temperature, “cold work”).
– On annealing (‘hard work”),
dislocations leave the slip planes and
climb into the positions which are
closer to equilibrium such as
networks.
– 1960s Structural
geologists concerned with
deformation of rocks (slow
to respond to the new
concept) (Turner and
Weiss, 1963 Structural
Analysis of Metamorphic
Tectonites)
– 1965, McLaren and
Phakey, dislocations in
thin milky vein quartz.
– 1967, McLaren et al. first
direct observation of
dislocation and other
defects in thin foils of
deformed specimens.
Purpose of study dislocation microstructures in a wide
range of naturally and experimentally deformed
minerals and rocks are:
– (1) to determine the deformation mechanism;
– (2) to interpret the microstructure observed in
naturally deformed specimens;
– (3) to determine their deformation theory.
Deformation of “wet” synthetic quartz
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Dislocations in a deformed region where the original density of clusters was low. There
are two sets of dislocations. It appears no clusters or strain-free bubbles in specimens
deformed in low temperature. The observation suggests that the water (originally in the
cluster) is now distributed in the dislocation cores, assuming that it has not diffused out of
the crystal. The ragged fine structure of these dislocation images suggests the presence of
many pinning points along the dislocations, which actually produce a drag on the
dislocation glide.
Significant microstructural change of deformed crystals after annealing.
Dislocations are smoothly curved, and many have interacted to form
network; also much debris of small dislocation loops, and noticeable
decrease in dislocation density – indicate that considerable recovery due to
dislocation climb (has occurred during annealing). Annealed specimens
show many bubbles (both isolated and linked by dislocations). It appears
to confirm that specimens deformed in low temperatures the water
originally in the cluster is distributed in the dislocation cores.
Small bubbles are more
easily identified in out-offocus phase contract images
in which the dislocations
are out of contrast.
Deformation of Carbonates
(1) Microstructures in
deformed calcite
The twin boundaries commonly
contain closely spaced arrays of
twinning dislocations, and the
twinned lamellae usually contain
numerous glide dislocation generated
by the twinning. The untwined matrix
may contain only a low density of
preexisting dislocations.
However, deformation twinning can
generate glide dislocations in both the
twin lamellae and the matrix, due to
the need to relax the intense stress
produced by he shape change at the
surface near the tip of a moving twin
lamella.
Deformation of Carbonates
(1) Microstructures in
deformed dolomite
The deformation characteristics of
dolomite are markedly different
from those of calcite.
Not only are the twin laws different,
but twinning in dolomite occurs
only at temperature above 250oC.
The lower dislocation density in
twinned dolomite and at twin
intersections is perhaps due to the
greater ease of stress relaxation at
the higher temperatures required
for twinning.
Deformation of Olivine
- Olivine is the major mineral
constituent of the upper mantle
and presumably dominates the
flow of the asthenosphere.
Thus of great geophysical and
geological interest.
- Olivine deformed at
strain rate of 10-4 and 10-5 sec-1,
the dislocation configuration
vary considerably with
temperature.
Mineralogical Application (2) - HRTEM
• Determination of the Atomic
Structure
- In TEM, eD pattern is
obtained in the back focal plane
of the objective lens. This
similar to the case of XRD, the
Fourier transform of
electrostatic potential
differences in the specimen
which corresponds to the
electron density distribution.
- But in contrast to XRD, the
TEM can be used to obtain the
inverse transform of diffraction
pattern experimentally in the
image plane without losing the
phase information.
- Two dimensional images of
the electron density with
resolution of better than 0.14
nm in which the contrast from
single atoms can be recognized.
Z-projection of the electrostatic potential difference in tourmaline (left), a
close correspondence to the crystal structure as determined by XRD (right)
TEM shows intensity variation from unit cell to unit cell (due to shortrange order), but cannot be seen with XRD.
XRD provide a more precise determination of the average electron density
in the unit cell of the lattice, while TEM resolves imperfections of the
lattice as local site occupancies.
(From Wenk, 1976)
• Application of HREM
• Graphite crystallization
• Carbon occurs ubiquitous
(organic debris in sedimentary
rocks, subcrystalline in low-grade
metamorphic rocks, and wellcrystallized graphite in igneous
and high-grade metamorphic
rocks.
• C in sedimentary rock is of
biological origin, and some such
rocks are older than the oldest
rocks that contain fossils. Thus,
study of graphite precursors
might provide insight into the
earliest life forms on the Earth.
• E.g., Laboratory annealing
experiments in an attempt to
understand the development of
graphite from noncrystalline
organic precursors.
• Application of HREM
• Cordierite (Mg2Al4Si5O18)
transformation
• Two polymorphs, with a
transformation temperature of
about 1450oC.
• Above 1450oC the equilibrium
form is hexagonal with space
group p6/mcc (the same space
group as beryl).
• Below 1450oC, it is
orthorhomibic, Cccm.
• Transformation occurs as a result
of Al-Si ordering among
tetrahedral sites that are
equivalent in the hexagonal
polymorph, thereby producing
the change in symmetry from
hexagonal to orthorhombic.
• HRTEM in Mineral Nomenclature
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International Mineral. Asso. Commission on New Minerals and Mineral Names
Requires the demonstration that structurally and chemically unique on the basis of XRD data
and chemical analyses, combined with determination of properties such as refractive indices,
and density.
The present international system generally functions well. However, HRTEM and other TEM
methods do raise questions for the future.
TEM can play an important role in description of new minerals.
The combination of TEM and XRD will be the best, i.e., complement each other.
Other Important Techniques Closely Related to HRTEM
• For each new detector that is fitted to an EM, a new sub-discipline of
electron microscopy is created.
• These subdisciplines are usually closely related to exiting well
established fields, e.g.,
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Cathodoluminescence (CL)
EDS
EELS
Electron loss near edge structure
(ELNES)
Photoluminescence (PL)
X-ray fluorescence spectroscopy
X-ray absorption studies
Near-edge-structure study
(XANES)
Near-edge X-ray absorption fine structure
(NEXAFS)
– Extended electron-loss fine structure Extended X-ray absorption fine
(EXELFS)
structure (EXAFS)
• Both of these have much in common with photoelectron spectroscopy
using either incident X-ray (XPS) or X-ray photoelectron spectroscopy.
(From Spence in Buseck, 1988)
• Unlike HRTEM (which records the positions of atoms),
spectroscopy is concerned with the measurement of
energies.
• Historically, the most important techniques are:
– (1) those that derive from the discovery of the photoelectric
effect (such as XPS, UPS, ARPES, X-ray photoelectron
spectroscopy, and some EXAFS and XANES);
– (2) those that derive from the original Frank-Hertz
experiments (such as ELNES) and those based on opticalabsorption measurement (such as EXAFS and XANES).
• The important distinction is between absorption and
emission experiments.
• Spectroscopy provides important information in materials
characterization
Summary
• (1) This presentation provided a general review of the TEM application
in mineralogical (and geological) sciences.
• (2) It cannot be emphasized more that the importance of TEM in
mineralogical research. Description of domains, lamellae, and
dislocation provide geological information which cannot be obtained
with standard mineralogical and geochemical methods.
• (3) The TEM has applied to a wide variety of mineralogical and
geological problems ranging from a study of the crystal structure to the
dimension of the universe.
• (4) The TEM has become a standard instrument in such diverse
disciplines as crystallography, mineralogy, petrology, geophysics and
geotectonics, linking together all the earth sciences in an even more
general way the optical microscope.
• (5) Nevertheless, the progresses of TEM application in mineralogical
research has been slow (as compare with other areas of research).
More works are awaiting you to explore.
References
Many photographs, statement presented in the talk were taken from
the following books, and papers cited in those books:
– Wenk, H.-R., ed., 1976, ed., Electron Microscopy in Mineralogy,
Springer-Verlag.
– Buseck, P. R., 1988, co-eds., High-Resolution Transmission Electron
Microscopy and Associated Techniques, Oxford U Press.
– Mclaren A. C., 1991, Transmission Electron Microscopy of Minerals
and Rocks, Cambridge Univ. Press.
– Zvyagin, Boris B., (translated by Simon Lyse), 1967, ElectronDiffraction Analysis of Clay Mineral Structures, Plenum Press.
– Beutelspacher, H. and H. W. Van Marel, 1968, Atlas of Electron
Microscopy of Clay Minerals and their Admixtures, A Picture Atlas,
Elsvier Publishing Co.
– Gard, J. A. (ed.), 1971, The Electron-Optical Investigation of Clays,
Mineralogical Society (Clay Minerals Group).
Thank You
Muchas Gracias