cee 437 lecture 2 minerals - university of washington · bowen’s reaction series. weathering...
TRANSCRIPT
CEE 437 Lecture 10Minerals and Mineral
PropertiesThomas Doe
Outline
Rock cycleRock Forming MineralsMineral Physical PropertiesClay MineralsMicrofractures and Fracture Mechanics
Crustal Composition
Main Elemental GroupsSilicaAluminumFerro-MagnesianCa, Na, K
Rock Cycle
Metamorphic Rocks
Sedimentary Rocks
Igneous Rocks
Sediments
Lithification
Magma
Weathering, Erosion
Burial, metamorphism, recrystallization
Melting
Crystallization at depth or extrusion at surface
Burial, metamorphism, recrystallization
Mineral DifferentiationPlate tectonics and Igneous Processes
selective melting, selective recrystallizationdifferentiation by density
Weathering and ErosionSelective weatheringConcentration of quartz (pure Si02)Conversion of alumino-silicates to claysConcentration of soluble residues in seawater
DepositionCourser materials near sediment sourceFiner materials far from sediment sourceRedeposition of salts and solutes by evaporative (Na,KCl; CaSO4) or biological processes (CaCO3,; )
Subduction Zone – Island Arc
Evolution of Continents — North American Craton
Differentiation of Crustal Composition
Weathering differentiating towards higher Silica
Preferential melting of high-silica materials
Concentration of C, Ca, Na, K in sea and air
Original basaltic composition of crust
Carbonate concentrated by organic processes
Convergent Margin - Continental
Bowen Reaction Series
How to get many different rocks from one melt composition?Differentiation by selective crystallization and removal from system
Bowen’s Reaction Series
Weathering Cycle
Elemental Fates
Silicon tends to concentrate in crust — quartz is very long livedAluminum — transforms from feldspars to claysMica — transform to clays Fe-Mg-Ca-Na-K concentrate in some clays and micas, concentrate in oceans in biosphere
Sedimentary Differentiation
Sorting by Deposition MediumSorting by Energy
Mineral Definition
Naturally occurring material with unique combination of chemical composition and crystalline structureNatural non-minerals — glasses, coal, amorphous silicaPseudomorphs: diamond:graphite
Mineral Groups
Silicates: Major rock forming mineralsCarbonates: Minor in igneous rocks, mainly found in organic-derived rocks (limestones) and low-temperature cements and fracture fillings
Dissolution relationshipsSulfates (Gypsum) and Halides (salt, potash): Products of evaporation
Extreme dissolutionOxides
Weathering productsSulfides: Ores
Late stages of igneous melts, reducing conditionsAcid production, reactivity problems in concrete
Galena, PbS Graphite, C
Crystalline Structure of Calcite
Crystalline Symmetry Groups
Isomorphic Crystal Forms, Cubic System
Mineral Identification
DensityHardnessColor, luster (metallic, non-metalic, semi-metallic)Crystalline habitCleavageOptical microscopyMineral chemistry, x-ray diffraction
Hardness Scale
X-Ray Diffraction
Bragg’s Law
Physical Properties
Density (Gravity)Electrical Conductivity (Resisitivity)Thermal ExpansionStrengthElasticity (Mechanical properties,
Seismic/Acoustic VelocityRheology (Plasticity,Viscosity)
Properties and Mineral Symmetry
Tensor Properties of Crystals
Cubic Group
Lower Symmetry Groups
General Form for Heat Flow (for example)
Discussion: How to Rock Properties Relate to Mineral Structure
How will anisotropy vary with crystal symmetry class?
Rock Salt versus Quartz?How will aggregates of minerals (with same mineral behave?
Cubic versus non cubicRock fabricMaterial property contrasts
Rock Forming Minerals
Composition of CrustDominantly O, Si, Fe, Mg, Ca, Na, KNear surface importance of bio-processesSilicates from inorganic processesCarbonates mainly from shell-forming organisms
Crustal Composition
Main Elemental GroupsSilicaAluminumFerro-MagnesianCa, Na, K
Major Silicate Groups
Silicon Tetrahedronseparate tetrahedra — olivinesingle chains — pyroxenedouble chains — amphibolesheet silicates — micas and claysframework silicates — feldspars (with Al substitution), quartz as pure silica
Silica Tetrahedron
Forms of Silicates
Deformation Mechanisms
Effects on Physical Properties
AnisotropyProperties differ by direction
HeterogeneityProperties vary by location
Mineral properties may have strong anisotropy when crystals are alignedHeterogeneity may have strong mechanical effects when different minerals have different deformation properties
Weathering Fates
Feldspars to clays (clays, shales)Quartz endures (siltstones, sandstones)Calcium recirculated into carbonate minerals by organic processes (limestones)
Consequence:Over time, evolution of less dense more silicic continental crust
Clay Minerals
Extremely Important Mineral GroupSealsStabilityPore pressureChemical interactionSwellingSlaking
Confusion as both “Size” and “Mineral” Classification
Clay Rock Cycle
Clay Viewed from Electron Microscope
Clay Sources
WeatheringHydrothermal AlterationDepositionClay Transformations
Feldspar IlliteFerro-Magnesian ChloriteVolcanics (alkaline conditions) SmectiteVolcanics (acidic conditions) Kaolinite
Bentonite: plastic, highly swelling
Clay Units
From West, Geology Applied to Engineering, Prentice Hall, 1995)
Two and Three-Layer Clay Structure
From West, Geology Applied to Engineering, Prentice Hall, 1995)
Mixed Layer Clays
From West, Geology Applied to Engineering, Prentice Hall, 1995)
Minerals versus Rocks
Minerals ElementsAnisotropy from crystal structure
Elastic PropertiesThermal PropertiesOptical Properties
DeformationShear transformationsDislocations
Rock ElementsIntragranular
Anisotropy from fabricCrystal anisotropy if preferred orientationAnisotropy from bedding, foliation, flow structures
IntergranularCementsMicrocracks
HeterogeneityMineral compositionOther segregration processes
Translation of Mineral Properties to Rock Properties
Comparison of mineral properties to rock properties
Rocks have lower strength, especially tensile strengthAnisotropy of minerals and heterogeneity of minerals
ElasticityThermal expansionDiversity of mineral orientation
Creation of microcracks on mineral boundaries
LEFM: Linear Elastic Fracture Mechanics
Rocks are cracked materialsLEFM represents alternative view of material strength that accounts well for scale and geometric effectsImportant in brittle materials
Liberty ShipsComet passenger aircraft
Stress Intensity:
Y – geometric factor
σ – stressa – crack half length
Critical LEFM Elements
Stress IntensityConcentration of stress at Crack Tips
Fracture Toughness Measure of resistance to fractureDepends partly on plasticity of materialsLower in brittle materials