Optical minerology 1- polarization, refractive indices, relief, cleavage Flashcards
Why are minerals different?
different crystal structures and ionic compounds
What are 2 ways we can observe different structures allowing us to identify minerals?
X-Ray Diffraction (XRD)
Petrological (polarizing) microscope
What are the parts of a polarizing microscope?
Eye piece
Analyser
Objective
Microscope stage
Polarizer
Light source
What does optical minerology examine?
Intercation of minerals and visible light
What does the interaction of each mineral and visible light depend on?
Internal crystal structure of the mineral (optical crystallography)
What are the benefits of optical minerology?
Cheap
Quick
Easy to identify minerals and rock structure
What type of wave is visible light?
electromagnetic wave
How does energy vibrate in in relation to direction of travel?
perpendicularly
What 2 types of energy does light have?
electrical and magnetic (only need to think about electrical for this section)
What will the electrical part of light waves interact with in minerals?
the minerals electrical properties:
- bond strength
- electron densities
How do you find wave length of light waves?
distance between peaks (nm =x10^-9m)
What is frequency in regards to waves?
number of waves/sec to pass a given point (hertz cycles/sec)
What is amplitude in terms of light waves?
intensity of the light
What do you need to do to get consistent observations when shining rocks through rocks?
must be consistent thickness (30um or 0.03mm)
Why is 30um chosen as the thickness of rock sample for shining light through?
most minerals become optically transparent at this thickness
What is the difference between normal and polarized light?
Normal- vibrates all directions (reflected horizontal)
Polarized- only allows vertical light (reflected cut)
How is light made polarized on a microscope?
Normal light source with a polarized filter only allowing right to left (E-W) light through
Why isnt light an inherent property when using polarising light?
can change with with light type or intensity
Depending on crystal orientation will alter what light is absorbed and reflected
What is relief with minerals?
how well a material can be seen and distinguished from its surroundings
What will a low relief mineral be like?
very similar optical properties to mounting medium (epoxy)
Indistinct boundaries
What will a high relief mineral be like?
stand out
outer edge have distinct dark lines
What is refraction?
when the light path changes as it passes through a material
What does the amount of refraction depend on?
change of velocity between mineral and air
What is the formula for the refractivity index?
refractive index= velocity in air /velocity in mineral
