Download CEE 437 Lecture 2 Minerals

CEE 437 Lecture 2
Earth Materials I
Earth Structure and
Minerals
Thomas Doe
Outline




Global tectonic setting
Rock cycle
Rock forming minerals
Paper 1
Announcements

Paper and Quiz Schedule
Quiz 1 10-11
 Paper 1 10-18


Field Trips
Oct 23
 Nov 20


Office and Hours
132 G More
 Before class (3:00) or by appointment

Global Structure


Based mainly on seismic information and
meteorite compositions
Crust ~25-75 km depending varying under
continents and oceans
Velocity Variation with Depth
Global Structure
Development of Plate Tectonics



Evidence from ocean floor magnetism and ages
Evidence from seismicity
Evidence from cross-continent correlations of
rocks
Global Seismicity
Benioff Zone
Seafloor Spreading — Sediment
Ages
Sea-floor Spreading

Mantle convection driven
Evolution of Spreading Sea Floor
— Atlantic Analog
Convergent Margins


Ocean to Continent
Continent to Continent
Convergent Margin - Continental
Subduction Zone – Island Arc
Evolution of Continents — North
American Craton
North American Accretion
Rock Cycle
Crystallization at depth or
extrusion at surface
Igneous Rocks
Sediments
Lithification
Magma
Burial, metamorphism,
recrystallization
Weathering,
Erosion
Melting
Metamorphic
Rocks
Burial,
metamorphism,
recrystallization
Sedimentary Rocks
Mineral Differentiation

Plate tectonics and Igneous Processes



Weathering and Erosion





selective melting, selective recrystallization
differentiation by density
Selective weathering
Concentration of quartz (pure Si02)
Conversion of alumino-silicates to clays
Concentration of soluble residues in seawater
Deposition



Courser materials near sediment source
Finer materials far from sediment source
Redeposition of salts and solutes by evaporative (Na,KCl;
CaSO4) or biological processes (CaCO3,; )
Differentiation of Crustal
Composition
Weathering
differentiating
towards higher
Silica
Concentration of
C, Ca, Na, K in
sea and air
Carbonate
concentrated
by organic
processes
Preferential melting of
high-silica materials
Original basaltic
composition of crust
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
Crustal Composition

Main Elemental Groups




Silica
Aluminum
Ferro-Magnesian
Ca, Na, K
Elemental Fates




Silicon tends to concentrate in crust — quartz is
very long lived
Aluminum — transforms from feldspars to clays
Mica — transform to clays
Fe-Mg-Ca-Na-K concentrate in some clays and
micas, concentrate in oceans in biosphere
Differentiation in Crystallization
Versus Differentiation in Weathering
Slow Weathering
Quartz
Low Temperature,
High Silica, Low Fe Mg
Muscovite KFeldspars
Biotite
Amphibole
Pyroxene
Fast
Weathering
Olivine
Ca,Mg
Feldspars
High Temperature,
Low Silica, Hi Fe
Mg
Sedimentary Differentiation


Sorting by Deposition Medium
Sorting by Energy
Mineral Definition



Naturally occurring material with unique
combination of chemical composition and
crystalline structure
Natural non-minerals — glasses, coal,
amorphous silica
Pseudomorphs: diamond:graphite
Galena, PbS
Graphite, C
Crystalline Structure of Calcite
Crystalline Symmetry Groups
Isomorphic Crystal Forms, Cubic
System
Physical Properties





Density (Gravity)
Electrical Conductivity (Resisitivity)
Thermal Expansion
Strength
Elasticity (Mechanical properties,


Seismic/Acoustic Velocity
Rheology (Plasticity,Viscosity)
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 cubic
 Rock fabric
 Material property contrasts

Rock Forming Minerals

Composition of Crust
Dominantly O, Si, Fe, Mg, Ca, Na, K
 Near surface importance of bio-processes
 Silicates from inorganic processes
 Carbonates mainly from shell-forming organisms

Crustal Composition

Main Elemental Groups




Silica
Aluminum
Ferro-Magnesian
Ca, Na, K
Major Silicate Groups

Silicon Tetrahedron
separate tetrahedra — olivine
 single chains — pyroxene
 double chains — amphibole
 sheet silicates — micas and clays
 framework silicates — feldspars (with Al
substitution), quartz as pure silica

Silica Tetrahedron
Forms of Silicates
Deformation Mechanisms
Effects on Physical Properties

Anisotropy


Heterogeneity



Properties differ by direction
Properties vary by location
Mineral properties may have strong
anisotropy when crystals are aligned
Heterogeneity may have strong mechanical
effects when different minerals have different
deformation properties
Minerals versus Rocks

Minerals Elements

Anisotropy from crystal
structure





Rock Elements


Elastic Properties
Thermal Properties
Optical Properties


Deformation


Shear transformations
Dislocations
Intragranular

Intergranular



Anisotropy from fabric
Crystal anisotropy if preferred
orientation
Anisotropy from bedding,
foliation, flow structures
Cements
Microcracks
Heterogeneity


Mineral composition
Other segregration processes
Clay Minerals

Extremely Important Mineral Group
Seals
 Stability
 Pore pressure
 Chemical interaction
 Swelling
 Slaking


Confusion as both “Size” and “Mineral”
Classification
Clay Sources




Weathering
Hydrothermal Alteration
Deposition
Clay Transformations





Feldspar  Illite
Ferro-Magnesian  Chlorite
Volcanics (alkaline conditions)  Smectite
Volcanics (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)
Topics





Mineral Definition
Rock Forming Minerals
Physical Proprieties of Minerals
Mineral Identification
Mineral Lab
Clay Viewed from Electron
Microscope
Mineral Identification







Density
Hardness
Color, luster (metallic, non-metalic, semimetallic)
Crystalline habit
Cleavage
Optical microscopy
Mineral chemistry, x-ray diffraction
Hardness Scale
X-Ray Diffraction
Bragg’s Law
d

2 sin 
,   wavelength ,  incidence angle , d  lattice spacing
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
Engineering Implications

“Style” of geology and geo-engineering
problems varies with plate tectonic setting


Maturity of materials varies with plate tectonics
setting


Faulting, and structural complexity
Higher degree of more stable materials from sorting
by weathering
Geohazards vary with plate tectonic setting
Paper, 10-18




1. Physical Properties of Rocks and Crystals
Prepare a table of material properties for selected rock-forming minerals and
corresponding rock types. You should use both library and web sources. Choose
among the following concepts:
Role of mineral anisotropy and rock heterogeneity on strength and deformability
Role of mineral anisotropy and rock heterogeneity on mechanical effects during rock
heating and cooling (consider qualitatively the influence of differential responses)











Useful Ref: Carmichael, Handbook of Physical Properties of Rocks (CRC
Press)
2. Structure and Properties of Sheet Silicates
Define clay versus mica
Physical properties of clays
Differentiation of clays types
“Bad Actors”
3. The Rock Cycle and Its Influence on Rock Material Properties (non-geologists)
Differentiation by Plate Tectonics, Weathering and Deposition
Track clays through the Rock Cycle
4. Other topic (pre-approval recommended)