Optical minerology 1- polarization, refractive indices, relief, cleavage

Question 1

Why are minerals different?

Answer 1

different crystal structures and ionic compounds

Question 2

What are 2 ways we can observe different structures allowing us to identify minerals?

Answer 2

X-Ray Diffraction (XRD)
Petrological (polarizing) microscope

Question 3

What are the parts of a polarizing microscope?

Answer 3

Eye piece
Analyser
Objective
Microscope stage
Polarizer
Light source

Question 4

What does optical minerology examine?

Answer 4

Intercation of minerals and visible light

Question 5

What does the interaction of each mineral and visible light depend on?

Answer 5

Internal crystal structure of the mineral (optical crystallography)

Question 6

What are the benefits of optical minerology?

Answer 6

Cheap
Quick
Easy to identify minerals and rock structure

Question 7

What type of wave is visible light?

Answer 7

electromagnetic wave

Question 8

How does energy vibrate in in relation to direction of travel?

Answer 8

perpendicularly

Question 9

What 2 types of energy does light have?

Answer 9

electrical and magnetic (only need to think about electrical for this section)

Question 10

What will the electrical part of light waves interact with in minerals?

Answer 10

the minerals electrical properties:
- bond strength
- electron densities

Question 11

How do you find wave length of light waves?

Answer 11

distance between peaks (nm =x10^-9m)

Question 12

What is frequency in regards to waves?

Answer 12

number of waves/sec to pass a given point (hertz cycles/sec)

Question 13

What is amplitude in terms of light waves?

Answer 13

intensity of the light

Question 14

What do you need to do to get consistent observations when shining rocks through rocks?

Answer 14

must be consistent thickness (30um or 0.03mm)

Question 15

Why is 30um chosen as the thickness of rock sample for shining light through?

Answer 15

most minerals become optically transparent at this thickness

Question 16

What is the difference between normal and polarized light?

Answer 16

Normal- vibrates all directions (reflected horizontal)
Polarized- only allows vertical light (reflected cut)

Question 17

How is light made polarized on a microscope?

Answer 17

Normal light source with a polarized filter only allowing right to left (E-W) light through

Question 18

Why isnt light an inherent property when using polarising light?

Answer 18

can change with with light type or intensity
Depending on crystal orientation will alter what light is absorbed and reflected

Question 18

What is relief with minerals?

Answer 18

how well a material can be seen and distinguished from its surroundings

Question 18

What will a low relief mineral be like?

Answer 18

very similar optical properties to mounting medium (epoxy)
Indistinct boundaries

Question 19

What will a high relief mineral be like?

Answer 19

stand out
outer edge have distinct dark lines

Question 20

What is refraction?

Answer 20

when the light path changes as it passes through a material

Question 21

What does the amount of refraction depend on?

Answer 21

change of velocity between mineral and air

Question 22

What is the formula for the refractivity index?

Answer 22

refractive index= velocity in air /velocity in mineral

Question 23

What does a higher refractive index score mean?

Answer 23

the light travels slower through the mineral

Question 24

What is snells law?

Answer 24

the amount of bending of light as it travels from one medium to another

Question 25

What must be done to boost the understanding of relief besides just refractive index?

Answer 25

Becke line test

Question 26

How can cleavage be observed?

Answer 26

through microscope
good cleavage= clean break
poor cleavage - cracking / fracture

Question 27

What are opaque minerals?

Answer 27

minerals which light does not pass easily through which are even black in thin sections
Molecules with higher atomic density

Question 28

How are opaque minerals identified?

Answer 28

how light is reflected off them using a reflective light microscope