Lecture 1 & 2: Mineral Properties Mineral Definition: -Naturally ...
ESS221 Study Notes Condensed
Lecture 1 & 2: Mineral Properties Mineral Definition: -Naturally occurring -Made Inorganically (mostly) -definite but not fixed chemical composition -solid crystalline structure -homogenous substance *defracts X-rays Naming Minerals Family > Group > Species > Series > Polymorphs > Varieties Family: group related by composition. eg. Tectosilicates Group: related by similar atomic structure. eg. Quartz group Species: type of group eg. alpha or beta quartz Series: same structure, different composition eg. Olivine: forsterite Mg2SiO4 and fayalite Fe2SiO4 Polymorph: different structure, same formula eg. stishovite, coesite Variety: same mineral, with distinct physical properties eg. amethyst, rose quartz Silicate Minerals:
SiO4 4Si2O7 6Si6O18 12Si2O6 4Si4O11 6Si2O5 2SiO2
ESS221 Study Notes Condensed
Diagnostic Information Idiochromatic: color by essential elements Allochromatic: color by trace or minor elements Moh’s Scale: Logarithmic. Talc, Gypsum, Calcite, Fluorite, Apatite, Orthoclase, Quartz, Topaz, Corundum, Diamond 2.2 fingernail, 3.2 copper penny, 5.5 glass plate, 6.5 steel file, 7.0 streak plate. Cleavages: -basal: 1 direction. eg. micas -feldspar cleavage: 2 at right angles -cubic: 3 at right angles. eg. galena -calcite cleavage: 3 at non right angles -octahedral: 4 directions. eg. fluorite, diamond -6 directions: eg. sphalerite -prismatic: multiple directions parallel to one cleavage. Parting: breakage from an unusual point of weakness in the crystal due to twinning plane or exsolution. Sheen: adularescence - reflection from microscopic inclusions schiller - reflection from inner layers iridescence - reflection from interference of inner layers play of color - diffraction of light through spheres of SiO2 in Opal Other: specific gravity: eg. Galena taste, smell: Halite, Sulphur feel: graphite magnetism: magnetite reaction with HCl: carbonates fluorescence: wolframite Lecture 3: Earth Chemistry crust - 36km from continents, 10-13 from ocean. Upper = sed. 95% ig rock. 10 miles down. upper mantle - 36-410km. Olivines + pyroxenes + garnet transition zone - 410-660km spinels + majorite lower mantle - 660-2600km. silicate perovskite + ferropericlase D’’ layer - 2600-2900km. post perovskite outer core - 2900-5100km. liquid iron allow inner core - 5100-6400km. solid iron. Earth Minerals 116 elements found in nature. 8 make up 99% of crust: O, Si, Al, Fe, Ca, Na, K, Mg -most crustal are O based. Some elements are concentrated in specific minerals (eg. Zr in Zircon ZrSiO4) -39% plag, 12% alkali feld, 12% quartz, 11% pyroxenes, 8% non silicates. . . . .
ESS221 Study Notes Condensed
Solid Solution ions substituting for each other in a mineral. Rarely find pure mineral states. Occurs as size of ions and site change composition, as well as temp/press changes. Lecture 4: Mineral Chemistry and Bonding Covalent > Ionic > Metallic > Van Der Waal’s Ions can form from light, heat, and electron exchange between atoms. HCP: Hexagonal closed packing - ABABABABAB CCP: Cubic closed packing - ABCABCABCABC along [111] Pauling’s Rules 1: Coordination Principle: Large radius atoms pack around a small radius atom in as tight a configuration as possible such that the small atom never rattles around in the space. The large radius atoms are always in contact with the small radius atom. Based on Radius ratios and angles from them. 2: Electrostatic Valency Principle: Bond strength (e.v.) = ZC/C.N In a stable crystal structure, the total strength of the valency bonds that reach an anion from all the neighbouring cations is equal to the charge of the anion Eg. Mg2+O6: SMg-O = 2/6 = 1/3 Eg. Si4+O4: SSi-O = 4/4 = 1 3: Sharing of Polyhedral Elements I The more corners that are shared between two polyhedrons, then the closer together the cations are. This destabilizes the structure because of cation-cation repulsion. 4: Sharing of Polyhedral Elements II In a crystal containing different cations, those of high valence and small coordination number tend not to share polyhedral elements with each other. 5: Principle of Parsimony The number of essentially different kinds of constituents in a crystal tends to be small. Very few types of contrasting cation-anion sites. Lecture 5: Lattices and the Unit Cell lattice = grid /w motifs (single unit. eg. ion, atom) repeated regularly *which can be packed in a limited number of ways. They can be translated with an arbitrary origin. 2D unit cells: primitive or non-primitive (2 points +)
ESS221 Study Notes Condensed
Crystallographic Axes: A, B, C vs alpha, beta, gamma. Right Hand Rule: thumb is c, fingers are A, and arm is B along crystal with right hand. alpha(B,C). beta(A,C). gamma(A,B)
Crystal Systems
Bravais Lattices
P = prim. F = face I = Body C = c-axis
Lecture 6: Crystallographic Symmetry
Rotation: rotated on symmetry axis. 1, 2, 3, 4, 6 (360, 180, 120, 90, 60 degrees) Mirror Planes: reflection across mirror plane produces mirror image. ‘m’
ESS221 Study Notes Condensed
Center of Symmetry: a point (eg. face) can be inverted and passed through center of crystal to appear on the other side. 1 bar symbol. RotoInversions: rotation and passing through crystal. 1 bar = center of symmetry. 2 bar = mirror plane. 3 bar = 120RI, 4 bar= 90RI and 6bar=60RI Point groups: Triclinic: 1, 1bar Monoclinic: 2, m, 2/m Orthorhombic: 222, 2mm, 2/m,2/m,2/m Lecture 7: Miller Indices and More Crystallography Glide planes: translation and reflection Screw Axis: translation and rotation (like DNA) 14 Bravais lattice + 32 point group + 2 translation symmetry = 230 space groups. Miller Indices (hkl) = face {hkl} = family of faces [hkl] = direction of faces based on where a face intersects the axes. Usually use the number 1 to represent the faces when you have no coordinates. unit face = largest face that intersects all 3 axes.
ESS221 Study Notes Condensed
*hexagonal system has 4 axes [hkil] but one of the first three values are redundant, so you only need 3 to form a plane. Crystal form: a group of like crystal faces related by elements of symmetry. General form = faces intersect different axes at different lengths, which can describe multiple faces on a crystal. eg {111} Special form = all other forms present *faces that define the form need to have all positive intercepts. There are 48 total forms. 32 general ones. 10 special, 6 open.
Zones set of faces parallel to a common direction (zone axis [hkl]) Lecture 8: Crystallization Crystal Growth: atoms in solution no longer have enough energy to dissolve, so they form crystals. These grow based on available atoms. -> many form from water solutions (eg. quartz or NaCl) growth based on space freedom, time, and nutrients available. -> different minerals can grow simultaneously or sequentially on same rock Pseudomorphs: minerals
get
exposed to solutions, react, and recrystallize differently. Eg. Azurite can change to malachite, but maintain azurite appearance.
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Epitaxis: crystalline growth of one substance over another of different composition. Parallel Growths: intergrowths of same composition Twinning: Symmetrical intergrowth of 2+ of the same crystal formed by eroding during crystallization. -> contact twins - planar composition surface separates twins. eg. If twin plane is symmetric at 180 degrees, they are growing in opposite directions -> lamellar twins - repeated/continous contact twins (polysynthetic) Eg. Microcline tartan twins -> cyclic twins - repeats of contact twins in rotation at 30, 45, 60, 90 angles -> penetration twins - into and out of each other. eg. fluroite cubic or staurolite cruciform twins.
Lecture 9: Imaging Methods Qualititative = detective and identifying chemical constituents -Scanning Electron Microscopy -X-ray Diffraction Quantitative = %compositions -Electron Microprobe Analysis -X-ray D -Secondary Ion Mass Spectrometry -X-ray Fluorescence Electromagnetic Waves X-rays have photon energies between 100eV and -100eV. We use hard X-rays for diffraction between 1keV and -120 keV. wavelengths of X-rays are comparable to atom sizes, so this helps probe structural arrangements of atoms. X-ray Tube 1. Cathode emits electrons into vacuum 2. Anode collects them, making electrical flow beam 3. High V power source connects to cath/anode to accelerate ions 4. X-ray spectrum depends on anode material and voltage as anode rotates. X-ray diffractometers -when electrons have enough energy to dislodge from shell, X-ray spectra are produced. It can interpret a ratio of intensity Ka1:Ka2:Ka3 (a=alpha) Bragg’s Law: Used to interpret a X-ray diffraction data nλ = 2d sin(Ɵ) where: λ = wavelength of X-ray Ɵ = scattering angle
ESS221 Study Notes Condensed
n = order of diffraction peaks d = distance between successive
atomic planes
Parallel incident X-rays and scattering angles can help determine the distances
Powder Diffraction PXRD is most widely use as powder sample gives more SA and useful when crystal is liquid suspended or in polycrystalline solids -can help define unit cell with a referencial lattice (hkl) -can detect purity -works best in isometric crystals -not helpful for multi-phase minerals -> check large peaks that don’t have overlaps Single Crystal Diffraction Shoots x-ray through fibreoptic taper that gets detected as visible light -> can tell us where atoms are located, and their bond positions and types, as well as symmetry and size of unit cell. Synchroton radiation and Neutron Diffraction - big ass expensive equipment that does stuff. Lecture 10 - Light and Optical Microscopy 1 Light = waves + photons -> single wvlength = monochromatic -> we interpret vis. light as colors Wave theory: 1. visible light travels in a straight direction 2. It virates at angles to the direction of propagation, forming waves. frequency = number of waves that pass fixed point per unit time velocity = frequency x wvlength Refractive index: E = hν = hC/λ where E = energy, h = Planck's constant 6.62517 x 10-27 erg.sec, ν = frequency, C = velocity of light = 2.99793 x 1010 cm/sec, λ = wavelength RI = ratio of speed of light in a vacuum (C) to speed of light in a material that it passes through. Will always be above one since the speed will always be greater in a vacuum. If light strikes a material of a different RI, some light will reflect, and some will refract into the material.
ESS221 Study Notes Condensed
Snell’s Law: ni x sin (i) = nr x sin (r)
Critical angle: refracted ray travels along the interface between two substances, at an angle Ic Optics -use thin sections of rock XPL: analyzer + polarizer. shows vibrant colors ->isotropic minerals go extinct in XPL, anisotropic ones still have light. PPL: 1 wvlength of light, only have polarizer below the stage in. Lecture 11, 12, 13: Optics Relief: measure of relative difference between RI of mineral and epoxy -> seen in PPL Epoxy = 1.55, Quartz = 1.54, Fluorite = 1.433, Topaz = 1.6 -> detect with Becke Line test: -lower stage in PPL. -if line moves into crystal, it is high RI, if it moves out, it is low relative RI Color and Pleichroism rotate stage to observe color changes in pleichroism (eg. biotite green/brown - colorless) exists in anisotropic minerals Isotropic = light velocity travels in same direction at all axes. Isometric minerals show this. extinction in XPL Anisotropic = light velocity travels in different directions. -> Uniaxial = 2 directions a = b, c unique; hexagonal, trigonal, tetragonal -> Biaxial = 3 directions; orthorhombic, monoclinic, triclinic -> appear extinct at 90 degrees in XPL Birefringence bright colors under XPL when 2RI combine from slow and fast rays from different axes. δ = nhigh - nlow. Look for highest interference colors in XPL and quantify on Michel Levy. Uniaxial Indicatrix Omega/ordinary ray vs. Extraordinary/Epsilon Ray.
ESS221 Study Notes Condensed
-> Extraordinary can reach up to 90 degrees from c-axis. -> positive: E > O, negative: O > E Extinction and Interference Colors Extinction = always in XPL for isotropic. 4 times at 90 degrees in anisotropic rotations. Isogyres = interference figures. These show up with bertrand lens placed. BURP: blue upper right positive YURN: yellow upper right negative -> use gypsum plate to see these. -> fast + fast = addition -> fast + slow = subtraction -> applies to uniaxial and biaxial. -> biaxial interference figures are weirdly thick and curvy -> 2V angle is determined by how straight or curved the line of an isogyre appears in the center of the view. Lecture 14: Stability and Phase Diagrams Phase Diagrams: 1 component - polymoprhs 2 components - binary 3 components - ternary Minerals Formation -hydrothermal processes in vents. Eg. sublimation from vapor -diagenesis (rock changes and sediment change from weathering at low pressure) reacts solids together -metamorphism - also reacts solids together -evaporation -weathering -biological activity -crystallization from liquid magma to form igneous rock
Geothermal Gradient: the way pressure/temp varies on/in the Earth. -> P, T, and compositional variables all determine stability of minerals Systems: part of universe under consideration Isolated = cannot exchange energy/mass with surroundings closed = cannot exchange mass, but can exchange energy. Phase = physically separated part of a system by distinct physical and chemical properties. -> polymorphic phase diagrams Components = different chemicals belonging to multiple phases. -> binary, ternary, etc. . . diagrams
Phase Diagram by P vs T for CaCO3
Phase Diagram for Al2SiO5
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-Al coordination changes [4], [5], [6] as P is higher
Carbon Phases: While it needs high P to become diamond, the reverse process back to graphite takes longer, hence diamond is found on the surface
SiO2 quartz phases: coordination goes from [4] -> [5] -> [6] -> Stishovite can return back to coesite easily as pressure drops on surface after a meteor.
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Multiple components: Solid Solution -> Olivines, forsterite and fayalite -> above liquidus = all melt -> below solidus = all solid -> between is solid + melt. Hence, olivine is a complete solid solution between Magnesium and Iron. As well as Albite and anorthite feldspar solutions.
Lecture 15 and 16 : Mineral Behavior Exsolution: An initially homogenous mineral separates into different compositional domains due to drop in T. Can unmix to form patches. Visible under XPL. Eg. Al2SiO5 mixtures will exsolve when allowed to cool slowly in Na-K feldspars, forming ‘perthite’ due to differences in atomic radii of Na and K. Also causes tartan twinning. Metamictization: Ordered mineral structure damaged by radiation from radioactive elements within the mineral. Happens in man U and Th minerals Polymorphism: Mineral structure adjusts as P-T conditions change
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-> reconstructive - abrupt changes, which means it takes longer to change back. eg. Diamond and graphite, or coesite stishovite (lesser extent) -> displacive - gradual changes, less energy to change back when conditions change. Eg. high and low quartz changes -> produces Dauphine twins in quartz as bonds kink.
Polytypism: Polymorphs that only differ in the ways they stack -
Transformation twinning • KAlSi3O8 minerals include high T sanidine, lower T orthoclase, and lowest T microcline • Microcline shows ‘tartan’ twinning (under xp) caused by the loss of two symmetry elements as temperature drops Deformation twinning • Crystal is deformed with application of mechanical stress causing atomic slip and gliding or deformation twins
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Pyroxenes: ortho-p’s are orthorhombic. Clinopyroxenes are monoclinic. Calcium changes structural abilities from Ortho -> Clino -> Wollastonite
Lecture 17: Rocks and Minerals of the Earth Seismology- study of earthquakes P waves = slinky compressed S waves = shear waves, ropelike. do not travel through liquid
Experimental Petrology: -> simulate igneous or metamorphic conditions in a lab using high P/T furnaces to examine melting, crystallization, and diffusion eg. Diamond Anvil Cell. High T = graphite so diamond gets replaced each time
We can study crystal formations from meteorites which were formed and collided at high pressure and temperature. -> tells us about the core
ESS221 Study Notes Condensed
-> core produces geodynamo, which are convections that deflect solar winds. -> inner core is mostly Fe, and some Ni. Outer core includes those + some light elements based on density measurements. -> Fe crystallizes in a [8] coordination with BCC packing at low P-T -> changes to hcp and [12] coordination in outer core. ->information on lower mantle -> All Si coordinations are [6] in silicate perovskites. (Mg,Fe)SiO3 -> also 6 coordinated in stishovite and magnesio-wustite. (Mg, Fe)O -> If Mg/Fe are available, stishovite wont form -> hence magnesio perovskite is most abundant -> information on transition zone ->[4] and [6] coordinations of Si. Above all [4] and below all [6] -> Pyroxenes transform to garnet structure (majorite) at low density -> Spinels are important in shallow upper mantle -> olivine -> wodsleyite -> ringwoodite at high densities -> Upper mantle info -> 60% olivine, 25% pyroxene, 10% Al component of plagioclase, garnet, or spinels. -> can be observed directly from pipes and deep valley -> Silicate crust info -> 12 tectonic plates in constant motion due to mantel convections -> Oceanic are thinner (10km) -> Continental are thicker and have sed, ig, and meta rocks (30-50km)
Lecture 18: Rocks Igneous intrusive (plutonic): formed from cooling magma within crust surrounded by other rock. -> slow cooling produces large crystals with easily identifiable minerals such as quartz, plag, K-spar ->large grain size extrusive (volcanic): partially melted rock within mantle and crust forms magma which is less dense than surrounding rock so it rises (called lava when on surface). -> made of different composition around the world and can incorporate other rocks as it ascends -> fast cooling, small crystals that need a microscope to see
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Magma Compositions Felsic - granite and rhyolite. 60% or more weight in SiO2, light colored minerals Intermediate - diorite and Andesite. 50-60% SiO2 Mafic - gabbro and basalt. 18% MgO. Bowen’s Reaction Series continuous - changes in composition discontinuous - changes in structure and composition -> Can make intrusive diagrams of compositions for each mineral type and polymorph or series.
Metamorphism Sum of all changes in a rock as a result of environmental changes that occur without melting the rock. Depends on form of protolith, the original rock. -> subduction-related: ocean crust forms undearneath crust at plate boundaries created high P and low T and metamorphic rocks ->Regional Metamorphism: large regions subjected to high P and T due to crustal thickening and mountain building as rock gets buried. Found in precambrian shields ->Contact Metamorphism: made from heat associated with igneous plutons intruding into the crust. T decreases away from plutons creating a contact aureole between them. ->Shock Metamorphism: caused by sudden extreme pressure, like a structural fault or meteorite impact as high pressure makes minerals form instantly. -these can all be mapped on a metamorphic gradient based on how fine (low) the grains are due to pressure and temperature changes. -as metamorphism gradually occurs, the texture of rock changes forming porphyroblasts (swirls in opposite directions forming circles in a rock face. -> long grains tend to form lineations -> when they are platy they tend to foliate due to various degrees of folding. Protoliths: Metabasites Shows regional metamorphisms and basaltic protoliths. Sedimentary Rocks: -formed from fragments of other rocks (siliciclastic), or from minerals precipitated chemically (chemical),
ESS221 Study Notes Condensed
or from accumulation of organic matter (biogenic). ->all near earth surface covering
75% of exposed surface. Siliciclastic - erosion of rocks carry away particles (clasts) to deposit them somewhere. Can be buried underwater or heated and compacted together (lithification) to form rocks. -> heavy particles get carried short distances. sand > silt distances they can travel.
> mud in terms of
Chemical - large crystal precipitates in water filled cavities over time with ion-rich fluid. Chemical weathering happens a lot in clays evaporites: evaporation from lakes exceed water input from rain and other river sources, so rocks get unburied from water and form on ledges. Biogenic - living organisms extract ions dissolved in water to form shells/bones. -> eg. coral formed by calcerious minerals get buried overtime as they die. They get compacted and sedimented leading to limestone formation. Can form a lot of Carbonates. 95% of sed is sandstone, mudstone, and limestone. Quartz is uniquely common while being difficult to form in these ways. Lithification -> sed cemented together by precipitates due to T, P, pH, or biological activity -> rocks undergoing diagenesis
biogenic:
siliciclastic
Lecture 1 & 2: Mineral Properties Mineral Definition: -Naturally occurring -Made Inorganically (mostly) -definite but not fixed chemical composition -solid crystalline structure -homogenous substance *defracts X-rays Naming Minerals Family > Group > Species > Series > Polymorphs > Varieties Family: group related by composition. eg. Tectosilicates Group: related by similar atomic structure. eg. Quartz group Species: type of group eg. alpha or beta quartz Series: same structure, different composition eg. Olivine: forsterite Mg2SiO4 and fayalite Fe2SiO4 Polymorph: different structure, same formula eg. stishovite, coesite Variety: same mineral, with distinct physical properties eg. amethyst, rose quartz Silicate Minerals:
SiO4 4Si2O7 6Si6O18 12Si2O6 4Si4O11 6Si2O5 2SiO2
ESS221 Study Notes Condensed
Diagnostic Information Idiochromatic: color by essential elements Allochromatic: color by trace or minor elements Moh’s Scale: Logarithmic. Talc, Gypsum, Calcite, Fluorite, Apatite, Orthoclase, Quartz, Topaz, Corundum, Diamond 2.2 fingernail, 3.2 copper penny, 5.5 glass plate, 6.5 steel file, 7.0 streak plate. Cleavages: -basal: 1 direction. eg. micas -feldspar cleavage: 2 at right angles -cubic: 3 at right angles. eg. galena -calcite cleavage: 3 at non right angles -octahedral: 4 directions. eg. fluorite, diamond -6 directions: eg. sphalerite -prismatic: multiple directions parallel to one cleavage. Parting: breakage from an unusual point of weakness in the crystal due to twinning plane or exsolution. Sheen: adularescence - reflection from microscopic inclusions schiller - reflection from inner layers iridescence - reflection from interference of inner layers play of color - diffraction of light through spheres of SiO2 in Opal Other: specific gravity: eg. Galena taste, smell: Halite, Sulphur feel: graphite magnetism: magnetite reaction with HCl: carbonates fluorescence: wolframite Lecture 3: Earth Chemistry crust - 36km from continents, 10-13 from ocean. Upper = sed. 95% ig rock. 10 miles down. upper mantle - 36-410km. Olivines + pyroxenes + garnet transition zone - 410-660km spinels + majorite lower mantle - 660-2600km. silicate perovskite + ferropericlase D’’ layer - 2600-2900km. post perovskite outer core - 2900-5100km. liquid iron allow inner core - 5100-6400km. solid iron. Earth Minerals 116 elements found in nature. 8 make up 99% of crust: O, Si, Al, Fe, Ca, Na, K, Mg -most crustal are O based. Some elements are concentrated in specific minerals (eg. Zr in Zircon ZrSiO4) -39% plag, 12% alkali feld, 12% quartz, 11% pyroxenes, 8% non silicates. . . . .
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Solid Solution ions substituting for each other in a mineral. Rarely find pure mineral states. Occurs as size of ions and site change composition, as well as temp/press changes. Lecture 4: Mineral Chemistry and Bonding Covalent > Ionic > Metallic > Van Der Waal’s Ions can form from light, heat, and electron exchange between atoms. HCP: Hexagonal closed packing - ABABABABAB CCP: Cubic closed packing - ABCABCABCABC along [111] Pauling’s Rules 1: Coordination Principle: Large radius atoms pack around a small radius atom in as tight a configuration as possible such that the small atom never rattles around in the space. The large radius atoms are always in contact with the small radius atom. Based on Radius ratios and angles from them. 2: Electrostatic Valency Principle: Bond strength (e.v.) = ZC/C.N In a stable crystal structure, the total strength of the valency bonds that reach an anion from all the neighbouring cations is equal to the charge of the anion Eg. Mg2+O6: SMg-O = 2/6 = 1/3 Eg. Si4+O4: SSi-O = 4/4 = 1 3: Sharing of Polyhedral Elements I The more corners that are shared between two polyhedrons, then the closer together the cations are. This destabilizes the structure because of cation-cation repulsion. 4: Sharing of Polyhedral Elements II In a crystal containing different cations, those of high valence and small coordination number tend not to share polyhedral elements with each other. 5: Principle of Parsimony The number of essentially different kinds of constituents in a crystal tends to be small. Very few types of contrasting cation-anion sites. Lecture 5: Lattices and the Unit Cell lattice = grid /w motifs (single unit. eg. ion, atom) repeated regularly *which can be packed in a limited number of ways. They can be translated with an arbitrary origin. 2D unit cells: primitive or non-primitive (2 points +)
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Crystallographic Axes: A, B, C vs alpha, beta, gamma. Right Hand Rule: thumb is c, fingers are A, and arm is B along crystal with right hand. alpha(B,C). beta(A,C). gamma(A,B)
Crystal Systems
Bravais Lattices
P = prim. F = face I = Body C = c-axis
Lecture 6: Crystallographic Symmetry
Rotation: rotated on symmetry axis. 1, 2, 3, 4, 6 (360, 180, 120, 90, 60 degrees) Mirror Planes: reflection across mirror plane produces mirror image. ‘m’
ESS221 Study Notes Condensed
Center of Symmetry: a point (eg. face) can be inverted and passed through center of crystal to appear on the other side. 1 bar symbol. RotoInversions: rotation and passing through crystal. 1 bar = center of symmetry. 2 bar = mirror plane. 3 bar = 120RI, 4 bar= 90RI and 6bar=60RI Point groups: Triclinic: 1, 1bar Monoclinic: 2, m, 2/m Orthorhombic: 222, 2mm, 2/m,2/m,2/m Lecture 7: Miller Indices and More Crystallography Glide planes: translation and reflection Screw Axis: translation and rotation (like DNA) 14 Bravais lattice + 32 point group + 2 translation symmetry = 230 space groups. Miller Indices (hkl) = face {hkl} = family of faces [hkl] = direction of faces based on where a face intersects the axes. Usually use the number 1 to represent the faces when you have no coordinates. unit face = largest face that intersects all 3 axes.
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*hexagonal system has 4 axes [hkil] but one of the first three values are redundant, so you only need 3 to form a plane. Crystal form: a group of like crystal faces related by elements of symmetry. General form = faces intersect different axes at different lengths, which can describe multiple faces on a crystal. eg {111} Special form = all other forms present *faces that define the form need to have all positive intercepts. There are 48 total forms. 32 general ones. 10 special, 6 open.
Zones set of faces parallel to a common direction (zone axis [hkl]) Lecture 8: Crystallization Crystal Growth: atoms in solution no longer have enough energy to dissolve, so they form crystals. These grow based on available atoms. -> many form from water solutions (eg. quartz or NaCl) growth based on space freedom, time, and nutrients available. -> different minerals can grow simultaneously or sequentially on same rock Pseudomorphs: minerals
get
exposed to solutions, react, and recrystallize differently. Eg. Azurite can change to malachite, but maintain azurite appearance.
ESS221 Study Notes Condensed
Epitaxis: crystalline growth of one substance over another of different composition. Parallel Growths: intergrowths of same composition Twinning: Symmetrical intergrowth of 2+ of the same crystal formed by eroding during crystallization. -> contact twins - planar composition surface separates twins. eg. If twin plane is symmetric at 180 degrees, they are growing in opposite directions -> lamellar twins - repeated/continous contact twins (polysynthetic) Eg. Microcline tartan twins -> cyclic twins - repeats of contact twins in rotation at 30, 45, 60, 90 angles -> penetration twins - into and out of each other. eg. fluroite cubic or staurolite cruciform twins.
Lecture 9: Imaging Methods Qualititative = detective and identifying chemical constituents -Scanning Electron Microscopy -X-ray Diffraction Quantitative = %compositions -Electron Microprobe Analysis -X-ray D -Secondary Ion Mass Spectrometry -X-ray Fluorescence Electromagnetic Waves X-rays have photon energies between 100eV and -100eV. We use hard X-rays for diffraction between 1keV and -120 keV. wavelengths of X-rays are comparable to atom sizes, so this helps probe structural arrangements of atoms. X-ray Tube 1. Cathode emits electrons into vacuum 2. Anode collects them, making electrical flow beam 3. High V power source connects to cath/anode to accelerate ions 4. X-ray spectrum depends on anode material and voltage as anode rotates. X-ray diffractometers -when electrons have enough energy to dislodge from shell, X-ray spectra are produced. It can interpret a ratio of intensity Ka1:Ka2:Ka3 (a=alpha) Bragg’s Law: Used to interpret a X-ray diffraction data nλ = 2d sin(Ɵ) where: λ = wavelength of X-ray Ɵ = scattering angle
ESS221 Study Notes Condensed
n = order of diffraction peaks d = distance between successive
atomic planes
Parallel incident X-rays and scattering angles can help determine the distances
Powder Diffraction PXRD is most widely use as powder sample gives more SA and useful when crystal is liquid suspended or in polycrystalline solids -can help define unit cell with a referencial lattice (hkl) -can detect purity -works best in isometric crystals -not helpful for multi-phase minerals -> check large peaks that don’t have overlaps Single Crystal Diffraction Shoots x-ray through fibreoptic taper that gets detected as visible light -> can tell us where atoms are located, and their bond positions and types, as well as symmetry and size of unit cell. Synchroton radiation and Neutron Diffraction - big ass expensive equipment that does stuff. Lecture 10 - Light and Optical Microscopy 1 Light = waves + photons -> single wvlength = monochromatic -> we interpret vis. light as colors Wave theory: 1. visible light travels in a straight direction 2. It virates at angles to the direction of propagation, forming waves. frequency = number of waves that pass fixed point per unit time velocity = frequency x wvlength Refractive index: E = hν = hC/λ where E = energy, h = Planck's constant 6.62517 x 10-27 erg.sec, ν = frequency, C = velocity of light = 2.99793 x 1010 cm/sec, λ = wavelength RI = ratio of speed of light in a vacuum (C) to speed of light in a material that it passes through. Will always be above one since the speed will always be greater in a vacuum. If light strikes a material of a different RI, some light will reflect, and some will refract into the material.
ESS221 Study Notes Condensed
Snell’s Law: ni x sin (i) = nr x sin (r)
Critical angle: refracted ray travels along the interface between two substances, at an angle Ic Optics -use thin sections of rock XPL: analyzer + polarizer. shows vibrant colors ->isotropic minerals go extinct in XPL, anisotropic ones still have light. PPL: 1 wvlength of light, only have polarizer below the stage in. Lecture 11, 12, 13: Optics Relief: measure of relative difference between RI of mineral and epoxy -> seen in PPL Epoxy = 1.55, Quartz = 1.54, Fluorite = 1.433, Topaz = 1.6 -> detect with Becke Line test: -lower stage in PPL. -if line moves into crystal, it is high RI, if it moves out, it is low relative RI Color and Pleichroism rotate stage to observe color changes in pleichroism (eg. biotite green/brown - colorless) exists in anisotropic minerals Isotropic = light velocity travels in same direction at all axes. Isometric minerals show this. extinction in XPL Anisotropic = light velocity travels in different directions. -> Uniaxial = 2 directions a = b, c unique; hexagonal, trigonal, tetragonal -> Biaxial = 3 directions; orthorhombic, monoclinic, triclinic -> appear extinct at 90 degrees in XPL Birefringence bright colors under XPL when 2RI combine from slow and fast rays from different axes. δ = nhigh - nlow. Look for highest interference colors in XPL and quantify on Michel Levy. Uniaxial Indicatrix Omega/ordinary ray vs. Extraordinary/Epsilon Ray.
ESS221 Study Notes Condensed
-> Extraordinary can reach up to 90 degrees from c-axis. -> positive: E > O, negative: O > E Extinction and Interference Colors Extinction = always in XPL for isotropic. 4 times at 90 degrees in anisotropic rotations. Isogyres = interference figures. These show up with bertrand lens placed. BURP: blue upper right positive YURN: yellow upper right negative -> use gypsum plate to see these. -> fast + fast = addition -> fast + slow = subtraction -> applies to uniaxial and biaxial. -> biaxial interference figures are weirdly thick and curvy -> 2V angle is determined by how straight or curved the line of an isogyre appears in the center of the view. Lecture 14: Stability and Phase Diagrams Phase Diagrams: 1 component - polymoprhs 2 components - binary 3 components - ternary Minerals Formation -hydrothermal processes in vents. Eg. sublimation from vapor -diagenesis (rock changes and sediment change from weathering at low pressure) reacts solids together -metamorphism - also reacts solids together -evaporation -weathering -biological activity -crystallization from liquid magma to form igneous rock
Geothermal Gradient: the way pressure/temp varies on/in the Earth. -> P, T, and compositional variables all determine stability of minerals Systems: part of universe under consideration Isolated = cannot exchange energy/mass with surroundings closed = cannot exchange mass, but can exchange energy. Phase = physically separated part of a system by distinct physical and chemical properties. -> polymorphic phase diagrams Components = different chemicals belonging to multiple phases. -> binary, ternary, etc. . . diagrams
Phase Diagram by P vs T for CaCO3
Phase Diagram for Al2SiO5
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-Al coordination changes [4], [5], [6] as P is higher
Carbon Phases: While it needs high P to become diamond, the reverse process back to graphite takes longer, hence diamond is found on the surface
SiO2 quartz phases: coordination goes from [4] -> [5] -> [6] -> Stishovite can return back to coesite easily as pressure drops on surface after a meteor.
ESS221 Study Notes Condensed
Multiple components: Solid Solution -> Olivines, forsterite and fayalite -> above liquidus = all melt -> below solidus = all solid -> between is solid + melt. Hence, olivine is a complete solid solution between Magnesium and Iron. As well as Albite and anorthite feldspar solutions.
Lecture 15 and 16 : Mineral Behavior Exsolution: An initially homogenous mineral separates into different compositional domains due to drop in T. Can unmix to form patches. Visible under XPL. Eg. Al2SiO5 mixtures will exsolve when allowed to cool slowly in Na-K feldspars, forming ‘perthite’ due to differences in atomic radii of Na and K. Also causes tartan twinning. Metamictization: Ordered mineral structure damaged by radiation from radioactive elements within the mineral. Happens in man U and Th minerals Polymorphism: Mineral structure adjusts as P-T conditions change
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-> reconstructive - abrupt changes, which means it takes longer to change back. eg. Diamond and graphite, or coesite stishovite (lesser extent) -> displacive - gradual changes, less energy to change back when conditions change. Eg. high and low quartz changes -> produces Dauphine twins in quartz as bonds kink.
Polytypism: Polymorphs that only differ in the ways they stack -
Transformation twinning • KAlSi3O8 minerals include high T sanidine, lower T orthoclase, and lowest T microcline • Microcline shows ‘tartan’ twinning (under xp) caused by the loss of two symmetry elements as temperature drops Deformation twinning • Crystal is deformed with application of mechanical stress causing atomic slip and gliding or deformation twins
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Pyroxenes: ortho-p’s are orthorhombic. Clinopyroxenes are monoclinic. Calcium changes structural abilities from Ortho -> Clino -> Wollastonite
Lecture 17: Rocks and Minerals of the Earth Seismology- study of earthquakes P waves = slinky compressed S waves = shear waves, ropelike. do not travel through liquid
Experimental Petrology: -> simulate igneous or metamorphic conditions in a lab using high P/T furnaces to examine melting, crystallization, and diffusion eg. Diamond Anvil Cell. High T = graphite so diamond gets replaced each time
We can study crystal formations from meteorites which were formed and collided at high pressure and temperature. -> tells us about the core
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-> core produces geodynamo, which are convections that deflect solar winds. -> inner core is mostly Fe, and some Ni. Outer core includes those + some light elements based on density measurements. -> Fe crystallizes in a [8] coordination with BCC packing at low P-T -> changes to hcp and [12] coordination in outer core. ->information on lower mantle -> All Si coordinations are [6] in silicate perovskites. (Mg,Fe)SiO3 -> also 6 coordinated in stishovite and magnesio-wustite. (Mg, Fe)O -> If Mg/Fe are available, stishovite wont form -> hence magnesio perovskite is most abundant -> information on transition zone ->[4] and [6] coordinations of Si. Above all [4] and below all [6] -> Pyroxenes transform to garnet structure (majorite) at low density -> Spinels are important in shallow upper mantle -> olivine -> wodsleyite -> ringwoodite at high densities -> Upper mantle info -> 60% olivine, 25% pyroxene, 10% Al component of plagioclase, garnet, or spinels. -> can be observed directly from pipes and deep valley -> Silicate crust info -> 12 tectonic plates in constant motion due to mantel convections -> Oceanic are thinner (10km) -> Continental are thicker and have sed, ig, and meta rocks (30-50km)
Lecture 18: Rocks Igneous intrusive (plutonic): formed from cooling magma within crust surrounded by other rock. -> slow cooling produces large crystals with easily identifiable minerals such as quartz, plag, K-spar ->large grain size extrusive (volcanic): partially melted rock within mantle and crust forms magma which is less dense than surrounding rock so it rises (called lava when on surface). -> made of different composition around the world and can incorporate other rocks as it ascends -> fast cooling, small crystals that need a microscope to see
ESS221 Study Notes Condensed
Magma Compositions Felsic - granite and rhyolite. 60% or more weight in SiO2, light colored minerals Intermediate - diorite and Andesite. 50-60% SiO2 Mafic - gabbro and basalt. 18% MgO. Bowen’s Reaction Series continuous - changes in composition discontinuous - changes in structure and composition -> Can make intrusive diagrams of compositions for each mineral type and polymorph or series.
Metamorphism Sum of all changes in a rock as a result of environmental changes that occur without melting the rock. Depends on form of protolith, the original rock. -> subduction-related: ocean crust forms undearneath crust at plate boundaries created high P and low T and metamorphic rocks ->Regional Metamorphism: large regions subjected to high P and T due to crustal thickening and mountain building as rock gets buried. Found in precambrian shields ->Contact Metamorphism: made from heat associated with igneous plutons intruding into the crust. T decreases away from plutons creating a contact aureole between them. ->Shock Metamorphism: caused by sudden extreme pressure, like a structural fault or meteorite impact as high pressure makes minerals form instantly. -these can all be mapped on a metamorphic gradient based on how fine (low) the grains are due to pressure and temperature changes. -as metamorphism gradually occurs, the texture of rock changes forming porphyroblasts (swirls in opposite directions forming circles in a rock face. -> long grains tend to form lineations -> when they are platy they tend to foliate due to various degrees of folding. Protoliths: Metabasites Shows regional metamorphisms and basaltic protoliths. Sedimentary Rocks: -formed from fragments of other rocks (siliciclastic), or from minerals precipitated chemically (chemical),
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or from accumulation of organic matter (biogenic). ->all near earth surface covering
75% of exposed surface. Siliciclastic - erosion of rocks carry away particles (clasts) to deposit them somewhere. Can be buried underwater or heated and compacted together (lithification) to form rocks. -> heavy particles get carried short distances. sand > silt distances they can travel.
> mud in terms of
Chemical - large crystal precipitates in water filled cavities over time with ion-rich fluid. Chemical weathering happens a lot in clays evaporites: evaporation from lakes exceed water input from rain and other river sources, so rocks get unburied from water and form on ledges. Biogenic - living organisms extract ions dissolved in water to form shells/bones. -> eg. coral formed by calcerious minerals get buried overtime as they die. They get compacted and sedimented leading to limestone formation. Can form a lot of Carbonates. 95% of sed is sandstone, mudstone, and limestone. Quartz is uniquely common while being difficult to form in these ways. Lithification -> sed cemented together by precipitates due to T, P, pH, or biological activity -> rocks undergoing diagenesis
biogenic:
siliciclastic
