cee 437 lecture 2 minerals thomas doe. topics mineral definition rock forming minerals physical...

CEE 437 Lecture 2Minerals

Thomas Doe

Topics

• Mineral Definition

• Rock Forming Minerals

• Physical Proprieties of Minerals

• Mineral Identification

• Mineral Lab

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 Symmetry Groups

Crystal Forms, Cubic System

Crustal Composition

Differentiation of Crustal Composition

Weathering differentiating towards higher Silica

Preferential melting of higher silica

Concentration of C, Ca, Na, K in sea and air

Original basaltic composition of crust

Carbonate concentrated by organic processes

Mineral Differentiation

• Plate tectonics– selective melting, selective recrytallization– differentiation by density

• Weathering and erosion

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

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

Major Silicate Groups

• Silicon Tetrahedron– separate tetraheadra — olivine– single chains — pyroxene– double chains — amphibole– sheet silicates — micas and clays– framework silicates — feldspars (with Al

substitution), quartz as pure silica

Forms of Silicates

Crystalline Structure of Calcite

Physical Properties

• Density (Gravity)

• Electrical Conductivity (Resisitivity)

• Thermal Expansion

• Strength

• Elasticity (Mechanical properties, – Seismic/Acoustic Velocity

• Rheology (Plasticity,Viscosity)

Deformation Mechanisms

Effects on Physical Properties• Anisotropy

– Properties differ by direction

• Heterogeneity– 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

Clay Viewed from Electron Microscope

Mineral Identification

• Density

• Hardness

• Color, luster (metallic, non-metalic, semi-metallic)

• Crystalline habit

• Cleavage

• Mineral chemistry, x-ray diffraction

Hardness Scale

X-Ray Diffraction

spacing lattice,angle incidence,wavelength,sin2

dd

Bragg’s Law