Crystal Growth & Defects

1. Crystal Growth & Defects:
Chapter 10 - Klein & Dutrow, 2007. Manual of Mineral Science, 23rd Edition.
Chapter 5 - Nesse, 2018. Introduction to Mineralogy, 3rd Edition.
Chapter 5 - Wenk & Bulakh, 2004. Minerals

2. Outline
• Crystal growth
• Growth by ?
• Growth from ?
• Mineral properties related to mineral growth
• Crystal defects
• Point, line, plane defects
• Mineral properties related to defects

3. Crystal growth: Growth from ?/Growth by ?
Igneous minerals from melt
Metamorphic minerals from solids
Sedimentary minerals
from solution
from vapor
from solid- hydrosphere
interaction
from solid- atmosphere
interaction
Supersaturation
by changing
concentration
by changing
temperature
by changing
pressure

4. Crystal growth
• Nucleation from solution
• Ex: NaCI dissolved in water
• by changing the concentration
• Evaporation → more Na+ and Cl- per unit volume →
supersaturation
• Slow evaporation → few crystals with characteristic shapes,
sharing a crystallographic orientation
• Rapid evaporation → many small nuclei form, randomly oriented
crystals
• by changing the temperature
• Hot water will dissolve slightly more NaCI than cold water.
• Lowering the temperature → supersaturation
• by changing the pressure
• The higher the pressure the more NaCI water can hold in solution
• Lowering the pressure → supersaturation
Klein & Dutrow, 2007

5. Crystal growth: Nucleation from solution
Application: solution mining
http://www.goldenpotash.com/project/solution-mining/ Google Earth

6. Crystal growth
• In magma, many ions and ionic groups exist in an uncombined state.
• Crystal nucleation and growth in a cooling magma are the result of two competing tendencies:
• Thermal vibrations that tend to destroy the nuclei of potential minerals
• Attractive forces that tend to aggregate atoms (and/or ions) into crystal structures
• As the temperature falls, the temperature effect diminishes, which allows the attractive forces to
dominate.

7. Crystal growth
http://www.snowcrystals.com
Fumarole on Kīlauea Volcano, Hawai‘i. (USGS)
• As the vapor is cooled, the dissociated atoms or molecules combine, eventually locking
themselves into a crystalline solid.
Ex: the formation of snowflakes from
air saturated with water vapor
Ex: the formation of sulfur crystals at the
base of fumaroles, or volcanic vents, from the
condensation of sulfur-rich gas

8. Crystal growth
Plummer et al., 2016

9. Crystal growth
• Most nuclei will not develop into larger
crystals because in a solution saturated
with respect to Na+ and Cl- ions, there is
also a tendency for nuclei to be
redissolved.
• These tiny crystals have a very large
surface area compared to their volume
• A large surface area implies that there are
many atoms on the outer surface of the
crystal with unsatisfied chemical bonds.
• If a nucleus is to survive, it must grow
rapidly enough to reduce its surface
energy (expressed as the ratio of surface
area to volume) and, consequently, its
solubility.
Monroe et al., 2007

10. Crystal growth
• When a nucleus reaches a critical size
through rapid deposition of further layers
of ions, it will have a high chance of
surviving and growing into a larger crystal.
• The energy of such a surface is lowered
when an atom attaches itself to it, and
the amount of energy released by such an
attachment depends on where the
attachment occurs.
• the energy of attachment is
• greatest at the corners
• intermediate at the edges
• and least in the middle of faces

11. Crystal growth
• The rate of growth determines which faces will become
prominent on a crystal; the slowest growing faces are manifest
in a crystal’s external morphology.
• {111} faces
• parallel to layers of Na+ and Cl−
• have a net positive or negative charge
• high surface energy (unsatisfied or distorted chemical
bonds )
• growth should be very fast because the greatest energy
reduction is achieved there
• each successive layer will be thicker and smaller
• {001} faces
• equal numbers of Na+ and Cl− exposed
• electrically neutral and lack a net electrical attraction for
cations or anions
• growth rate is relatively slow

12. Crystal growth: Mineral properties related to mineral growth
• Different atomic arrangements underlie different crystal planes or crystallographic directions.
• Properties that depend on direction in the crystal are called vectorial properties.
Vectorial properties
Discontinuous
vectorial properties
pertain only to certain planes or
directions within the crystal
Ex: growth rate, solution rate, and
cleavage
Continuous
vectorial properties
vary continuously with direction
within the crystal
Ex: hardness, thermal expansion,
electrical conductivity, and velocity
of light

13. Crystal growth: Discontinuous vectorial properties
• Cleavage
• takes place along those planes across which
the weakest bonding forces exist.
Cleavage planes are generally
the most widely spaced and
the least densely populated
Biotite
Graphite Diamond

14. Crystal growth: Discontinuous vectorial properties
• Growth rate
• Dendrites are an extreme
case of prevalent apex and
edge growth.
• The unique crystals
resemble a branching
plant, hence the name
‘‘dendrites’’.
• Ex: native gold, copper,
and silver and in
pyrolusite
Silver Copper
Halite

15. Crystal growth: Discontinuous vectorial properties
• Solution rate
• If a crystal is treated with a chemical solvent that attacks
it, the faces are etched or pitted.
• The shape of these pits is regular and depends on
• the structure of the crystal
• the face being etched
• the presence of chemical substitutions and inclusion
• the nature of the solvent
Etching
?

16. Crystal growth: Continuous vectorial properties
• Hardness
• Kyanite is strongly anisotropic, and its
hardness varies depending on
crystallographic direction, which is
considered an identifying
characteristic.
• The Mohs scale hardness of kyanite is
• ~4.5–5 when scratched in the
direction of [001]
• ~6.5–7 when scratched
perpendicular to this direction

17. Crystal growth: Continuous vectorial properties
• Thermal expansion
• Most minerals have unequal coefficients of
thermal expansion in different directions,
leading to poor resistance to thermal shock and
easy fracturing with heating or cooling.
• SiO2 glass
• an irregular internal structure
• more resistant to thermal shock
• Quartz
• crystalline
• less resistant to thermal shock
Wu et al., 2019

18. Crystal growth: Continuous vectorial properties
• Velocity of light
• The velocity of light in all transparent crystals, with the exception of those that are
isotropic, varies continuously with crystallographic direction.

19. Crystal defects
• Crystals are rarely flawless, and natural as well as
synthetic crystals commonly contain imperfections.
• Such imperfections affect
• growth rate
• crystal morphology
• basic properties of crystalline materials, such as:
• strength
• conductivity
• mechanical deformation
• color
• Imperfections in crystal structures are generally
classified by the dimension of their geometry as:
• point defects
• line defects
• plane defects
Defects
Point defects
Schottky
defects
Frenkel
defect
Impurity
defect
Line defects
Edge
dislocations
Screw
dislocations
Plane defects
Lineage
structures
Stacking
fault
Twinning

20. Crystal defects: Point defects – 0D
Point
defects
Schottky
defects
Frenkel
defect
Impurity
defect
Interstitial Substitutional
• Schottky defects
• vacancy defects
• Frenkel Defects
• mislocation defects
• Interstitial defects
• foreign ions that occupy
sites not normally used
• Substitution defects
• foreign ions that
substitute for one of the
normally present ions

21. Crystal defects: Line defects – 1D
• Slip does not involve simultaneously breaking all chemical bonds along the
slip plane.
• Rather, slip propagates through a crystal so that bonds are broken only along
a line defining the leading edge of the slip surface.
• The edges of the propagating slip surface, where chemical bonds are being
broken, are known as dislocation lines.
Line
defects
(Dislocations)
Edge
dislocations
dislocation line (DL) is
perpendicular to the Buergers vector
and
moves to the right (parallel to the
Buergers vector) as deformation
progresses.
Screw
dislocations
dislocation line (DL) is
parallel to the Buergers vector
and
moves to the back (perpendicular to the
Buergers vector) as deformation
progresses

22. Crystal defects: Plane defects – 2D
• Lineage structures
• In ideally perfect crystals,
• short-range + long-range order
• In less ideal (more real) crystals,
• Crystal made of a mosaic of domains that differ only
slightly in orientation.
• Each block in the mosaic has short-range order, but
the whole crystal lacks long-range order.
• This arrangement results in irregular zones or lines
of edge dislocations spaced at irregular intervals.
• These zones (or lines) will be irregular planar features
along which ions (or atoms) have an irregular
structural environment. These zones of irregularity
are known also as lineage structures. The structures
on either side of such lineages are slightly
misoriented with respect to each other.

23. Crystal defects: Plane defects – 2D
• Stacking fault
• a regular sequence of layers is
interrupted by an improperly
positioned layer
or
• one of the layers required in a
perfect crystal is missing

24. Crystal defects: Plane defects – 2D
• During the growth of a mineral, offsets to the atomic arrangement of the structure may occur that are
nonrandom. This results in the development of relatively common intergrowth patterns of well-
formed crystals (as well as anhedral grains).
Intergrowths
Different
compositions
Epitaxis
Same
composition
Parallel
growth
Symmetrical intergrowth
(Twinning)
Parallel intergrowth of barite crystals Two quartz crystals twinned across a mirror plane

25. Crystal defects
• Epitaxis
• Although the two compositionally distinct
intergrown crystals will tend to have
different structures (and unit cell sizes),
there are planes in their internal structures
where there is a good fit (or the least
amount of misfit) between them.
• This similarity in substrate reduces the
energy required for nucleation allowing for
such preferential overgrowth.

26. Crystal defects: Plane defects – 2D
• Parallel growth
• An aggregate of similar crystals with their crystallographic axes and faces parallel to each other is
called a parallel growth. Such aggregates, although they may at first appear to represent several
crystals, are a single crystal because the internal atomic structure remains unchanged in
orientation throughout the specimen.

27. Crystal defects: Plane defects – 2D
• Twinning
• a symmetrical intergrowth of two or
more crystals of the same
substance.
• The two or more individual crystals
of the twinned aggregate are related
by a symmetry element that is
absent in the original (untwinned)
crystal.
• The twin law that describes the twin
operation includes:
• specification of the twin
operation and
• identification of the
crystallographic plane or axis
associated with the twinning.
• Twin plane is never
parallel to a plane of
symmetry.
• The twin law is usually
expressed as “reflection
on {hkl}” or “twins on
{hkl},”
• Twin axis can never be an
axis of even rotation (two-,
four-, six-fold) if the twin
rotation involved is 180°.
• Twin law for a typical 180°
rotation is usually
expressed as “2-fold
rotation on [uvw]”

28. Crystal defects: Plane defects – 2D
Twins
Contact twins:
have a regular
composition surface
separating the two
individuals.
Penetration twins:
are made up of
interpenetrating
individuals having an
irregular composition
surface
(100) Contact twin in gypsum [001] penetration twin in orthoclase
Twins
Simple twins:
composed of just two
twin segments.
Multiple twins:
composed of three or more
segments repeated by the
same twin law.
Polysynthetic
twins
Cyclic twins
Polysynthetic twinning in plagioclase
by repeated reflection on {010}
Cyclic twinning in rutile by
repeated reflection on {011}

29. Crystal defects: Mineral properties related to defects
• Origin of color
• Origin of magnetic properties

30. Crystal defects: Origin of color
Color
• Color is the response of the eye to the visible light range of the electromagnetic spectrum.
• Color depends on the wavelengths that the mineral does not absorb.

31. Crystal defects: Origin of color
Origin of color
Crystal field transitions and Charge
transfer transitions
depend on having electrons on specific elements
Crystal field
transitions
electronic transitions to
higher energy level of
partially filled d orbitals of
the same ion
Charge transfer
transitions
electronic transitions to
higher energy levels on
adjacent ions
Color centers
depend on having electrons mislocated
Electron
color centers
Electron trapped in a vacant
site in a crystal
Hole
color centers
Electron is missing from its
normal location

32. Recall

33. Crystal defects: Origin of color
Crystal Field Transitions
• electronic transitions between partially filled d orbitals of transition elements.

34. Crystal defects: Origin of color
Factors influencing the color produced
by crystal field interactions are:
• the presence of a specific transition
element
• its oxidation state (valence), which
determines the number of electrons
in 3d orbitals
• the geometry of the site in which the
transition metal is housed,
(octahedral, tetrahedral, etc.)
• the strength of the crystal field
(charges on anions, distortion of
coordination polyhedra, etc.)
Peridot
Fe2+ in octahedral
Chrysoberyl
Fe3+ in octahedral
Almandine
Fe2+ in cubic
Fe Cr
Emerald
Cr3+ replace Al3+ in octahedral
There is a covalent component to the bonding
The absorption peaks are at lower energy
Ruby
• Cr3+ replace Al3+ in octahedral
• bonding is ionic

35. Crystal defects: Origin of color
Molecular orbital (charge transfer) transitions
• absorb electromagnetic radiation when
valence electrons are bumped to higher
energy levels on adjacent ions.
• Charge transfers may be:
• between two cations
• between an anion and a cation
• between two anions
X2+ + Y3+ ⇌ X3+ + Y2+

36. Crystal defects: Origin of color
Color centers
Electron
color centers
Electron trapped
in a vacant site in
a crystal
Hole
color centers
Electron is
missing from its
normal location
Electron color centers
Hole color centers

37. Crystal defects: Origin of color
Origin of color
Crystal field transitions and Charge
transfer transitions
depend on having electrons on specific elements
Crystal field
transitions
Electronic transitions to
higher energy level of
partially filled d orbitals of
the same ion
Charge transfer
transitions
Electronic transitions to
higher energy levels on
adjacent ions
Color centers
depend on having electrons mislocated
Electron
color centers
Electron trapped in a vacant
site in a crystal
Hole
color centers
Electron is missing from its
normal location

38. Crystal defects: Origin of magnetic properties
Origin of magnetic properties
• Magnetism derives from a property
of electrons called the magnetic
moment that results from their
spinning and orbiting motions.
• The sum of all the magnetic
moments of all the atoms in a
mineral gives it magnetism.

39. Crystal defects: Origin of magnetic properties
• Not attracted to even very powerful magnets;
in fact they are slightly repelled by them
Diamagnetic minerals
• Weakly attracted to strong magnets
• become magnetized in an external magnetic
field, but lose their magnetization when the
external field is removed
Paramagnetic minerals
Paramagnetism
Diamagnetism

40. Crystal defects: Origin of magnetic properties
Ferrimagnetism
• can retain magnetization for long periods of time
• Ferrimagnetism differs from ferromagnetism in that some atoms/ions in adjacent structural
sites have antiparallel magnetic moments
• The term antiferromagnetism is applied to materials in which antiparallel spins completely
cancel to yield zero net magnetic moment. It can be considered a special case of
ferrimagnetism.
Ferromagnetic – ferrimagnetic minerals
Ferromagnetism Antiferromagnetism

41. Crystal defects: Origin of magnetic properties

42. Crystal defects: Origin of magnetic properties

43. • Otálora, F., & García-Ruiz, J. (2014). Nucleation and growth of the Naica giant gypsum crystals.
Chemical Society Reviews, 43(7), 2013–2026. https://doi.org/10.1039/C3CS60320B
• Veritasium. (2021, January 27). These Pools Help Support Half The People On Earth.
https://www.youtube.com/watch?v=YMDJA4UvXLA
• Nikkei Asia. (2018, March 14). How to make pure, synthetic quartz.
https://www.youtube.com/watch?v=lzHqhNoyx2o
• Yancoal Canada. (2016, April 29). Yancoal Canada—Southey Potash Project.
https://www.youtube.com/watch?v=EHz_iRjWGPU
• FuseSchool - Global Education. (2015, December 4). Extraction Of Salt | Acids, Bases & Alkali’s |
Chemistry | FuseSchool. https://www.youtube.com/watch?v=_nPrlrS6g10
• uclaphysicsvideo. (2013, November 9). Paramagnetism and Diamagnetism.
https://www.youtube.com/watch?v=u36QpPvEh2c
• Uniclass Content. (2015, May 27). Concentration of Ores—Class 12.
https://www.youtube.com/watch?v=8oTdCGj334U
GEOL217