Lec 10 - Geol217 Fall2021 - OAR.pdf
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Crystal growth and defects can influence mineral properties. Crystals grow through nucleation and growth processes that depend on factors like temperature, pressure, and concentration changes. Point defects like vacancies or impurities, and planar defects like twins or dislocations influence properties. Color arises from electron transitions in d-orbitals of transition metals or between ions. Magnetic properties depend on whether electrons' magnetic moments cancel or add. Crystal structures and defects thus underlie important mineral characteristics.
![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](https://image.slidesharecdn.com/lec10-geol217fall2021-oar-220402141114/85/Lec-10-Geol217-Fall2021-OAR-pdf-16-320.jpg)
![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]”](https://image.slidesharecdn.com/lec10-geol217fall2021-oar-220402141114/85/Lec-10-Geol217-Fall2021-OAR-pdf-27-320.jpg)
![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}](https://image.slidesharecdn.com/lec10-geol217fall2021-oar-220402141114/85/Lec-10-Geol217-Fall2021-OAR-pdf-28-320.jpg)
Lec 10 - Geol217 Fall2021 - OAR.pdf
- 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