Chapter 12

Additional Analytical Methods

Analytical MethodsTechnique

TypeTechnique application

SubdivisionsSpecific

applicationDescription Destruction

Light microscopyGeneral surveys

Features larger than 1μm

TransmittedTransparent

mineralsPetrographic microscope –

light from below sampleNon

Reflected Opaque minerals (ore minerals)

Petrographic microscope – light from above sample

Non

DiffractionFurther identification,

lattice parameters and crystal structure

X-RayPowders of single

minerals or mixtures (heavy atom

position)

X-Ray beam scattered at differing intensities at different

anglesSemi

NeutronPowders of single

minerals or mixtures (light atom position)

Neutron beam scattered at differing intensities at different

anglesSemi

Particle Microscopy

High resolution imagingFeatures smaller than

1μm

Transmission Electron Microscopy

Images of structural defects: dislocations,

twin and phase boundaries

Accelerated (high voltage)electron beam deeply penetrates small area

Non

Scanning Electron Microscopy

Image sample morphology and

determine compositional

variations

Accelerated (low voltage)electron beam shallowly

penetrates large areaNon

Atomic Force Microscopy

Image arrangement of individual atoms in

surface of crystals

Measure electrostatic repulsion intensity of atoms in sample in close contact with atoms of a

crystal tip

Non

Analytical Methods

Technique Type

Technique application

SubdivisionsSpecific

applicationDescription Destruction

Chemical AnalysisAccurate chemical

compositions of minerals

Microprobe

Quantitative point analyses in polished sections; mostly only

Na and higher

Accelerated electron beam with two detectors: energy

dispersion and x-ray detector compared with standard

Non

X-Ray Fluorescence

Quantitative analyses of rock in

powder; gives chemical elements –

major and trace

High-energy polychromatic X-ray beam produces secondary fluorescent X-rays which are analysed for wavelength and

energy

Semi

Optical emission & absorption

Mostly for liquid sample quantitative chemical analyses

Light beam excite or absorb valence electrons from sample;

secondary beams dispersed into separate wavelengths of

measurable intensities

Complete

Mass spectrometry

Measure amounts of different isotopes - mainly radiometric

dating and determination of stable isotopes

Ionization of atoms, ions accelerated and into magnetic

field which deflects ions – degree of deflection dependant

on ion mass and charge

Complete

Analytical MethodsTechnique

TypeTechnique application

Subdivisions

Specific application

DescriptionDestructi

on

Spectroscopy Investigate structural

environments

Infrared & Raman

Information on symmetry, bond

lengths and angles,

coordination polyhedra

IR radiation or laser beam passed through sample

and intensity of light measured. Absorption of

light corresponds to energy differences of vibratinal levels in the

crystal

Non

X-Ray absorption

Compositional edges in mineral

grains

Measure the difference in absorption of X-rays

relative to the intensity of the rays

Non

Nuclear magnetic resonance

Determine the occupancy of an

element in different

structural sites

Nuclei of atoms in mineral spin to cause magnetic

field which is placed inside a large magnetic field.

Magnetic resonance when applied field = energy

difference in spin levels. Spesific for different

chemical and crystallographic environments

Non

Hoofstuk 13

Meganiese eienskappe van Vervorming

Spanning-vervorming Meganiese eienskappe – uitbeelding van kristal se

geskiedenis Definisies:

• Spanning (σ) Krag per oppervlakeenheid

• Distorsie (ε) Vervorming as ‘n gevolg van die spanning

• Vervorming Elasties

• As spanning verwyder sal vervorming na oorspronklike waarde terugkeer

Plasties or duktiel• Aktiewe dislokasies veroorsaak pemanente veranderinge in struktuur

en vorm, maar materiaal bly in verbinding (in tact) Werksverharding

• Spanning benodig om toenemende vervorming te veroorsaak verhoog vinnig soos wat die toenemende aantal dislokasies interfeer

Bros (Breking)• Materiaal bereik maksimum sterkte en verbrokkel heeltemal

Vervorming

Spanning op kristal Vervorm kristal op kristallografiese

glipvlakke (hkl) met verplasing in kristallografiese gliprigting [uvw]

Glip is nie oombliklik nie, maar plant voort langs die glipvlak soos wat die breking van bindings op mekaar volg en lei tot ‘n volledige verplasing van die twee dele van die kristal

Vervorming

Fig 13.2; 13.3; 13.4

Dislokasie mikrostrukture

Teenwoordig in meeste kristalle selfs by ideale groeitoestande

Aantal dislokasies neem in algemeen toe soos wat vervorming plaasvind

Ontwikkeling en voortplanting van dislokasies word beïnvloed mekaar asook ander hindernisse soos insluitsels

Lusse, diffusie van leё ruimtes (klim)

Dislokasie mikrostruktures

Lusse Fig. 13.6, 13.7

Dislokasie mikrostruktures

►Diffusie van leë ruimtes (klim)

►Fig. 13.8, 13.9

Meganiese vertweelinging

‘n Megaiese spanning kan deel van die kristal laat oorswaai in ‘n orientasie rondom ‘n seker vlak

Nuwe orientasie is verwant aan die oorspronklike orientasie deur ‘n spieёlvlak

Dus: Geometriese tweeling verhouding Vaste kleinskaalse vervorming, anders as

glip wat ‘n aaneenlopende Vervorming is en oor ‘n groot afstand kan plaasvind

Meganiese vertweelinging

Fig 13.10, 13.11