Lecture 5, 7, and 8

Question 1

Vermeer scale

Answer 1

• helps us to measure the angles accurately
• divided into 360

Question 2

Petrograd his microscope

Answer 2

• has occular, objective ( 4x, 10x, 2x and 40x)
• A small working distance and large working distance
• the larger the numerical aperture the higher the resolution

Question 3

Two observations used to transmit light in Petrographic microscopes

Answer 3

-orthroscopic illumination : light coming through reach the grains and all go in same direction
- perpendicular to the plane of specimens
Conospovic illumination
- different directions
- used condensing lense , demands Bertrand
It enable sis to magnified image

Question 4

Lecture 7

Question 5

Isotropic minerals and Anisotropic minerals

Answer 5

isotropic :
- atomic structure were arranged in same direction. Light travels through in all directions at same speed, same bonding but no preferred variation in direction
- perpendicular to the difference of propagation. Vibration of light in same way. Light refracts.
- ISO= same
- cubic is isotropic: garnet, spinel, sodalite, leucine, fluorite periclace, basalt
- remain dark throughout under cross polarized light

Anisotropic:
- different bonding, velocities in different directions.
- Anisotropic= not equal
- atomic structure are arrangements differently in all directions.
- have ability to rotate the plane of vibration of light
- splits light into two
Ex: quartz, plagioclase, beryl, olivine, kyanite, micas, gypsum,

Question 6

Measuring isotropic and Anisotropic under Ppl (lower polarizer) and xpl

Answer 6

• xpl: all isotropic minerals will be dark under xpl and still remain dark when light is vibrating. Orientation is not changing doesn’t transmit light
• the two light rays combine together
• ppl mineral will transmit light

Question 7

Color absorption under ppl

Answer 7

• Roygbv observed under ppl
• combination of two color under ppl in diff wavelengths of white light.
• result in different absorption of different wavelengths when xpl not inserted lead to absorption color,
• ex: is opaque minerals that is colorless or white.

Question 8

Cleavage

Answer 8

• cleavage lines formed along the line of breakage in minerals
  Ex: pyronene, amphiboles, plagioclase, biotite
• Olivine dont have cleaveges: it only has fractures. Fractures is irregular line of breakage but not repeated like cleavage

Question 9

Anisotropic minerals

Answer 9

• Split light into two, perpendicular to each other in both directions
  1. fast ray
  2. Slow
  The process of splitting light rays is called double refraction. One single rays reflected twice

Question 10

Lecture 8