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