Light and its behavoir

Question 1

What is the crystal’s refractive index n?

Sometimes reffered to R.I

Answer 1

Diagnostic feature
the ratio of the velocity (v) of light in a vacuum to the velocity in the crystal:
n = v(vacuum) / v(crystal)

Question 2

What is plane polarized (pp) light?

Answer 2

when all the waves vibrate in one direction perpendicular to a particular plane.

Using polarizing filter

Question 3

What is cross polarized light?

Answer 3

Using one more polarizing filter at the pp light (90 degree perpendicular to the forst filter), no light will pass through ecxept where the mineral grains are.

Mineral grains change the vibration direction of the light => pass through second filter.

Question 4

What are opague minerals?

Characteristics seen in PP light

Answer 4

Appear black in PP and XP light, even if rotating the stage.

graphite, oxides (magnetite and ilmenite), sulfides (pyrite, pyrrhotite)

Question 5

The phenomenon of retardation, Delta

Answer 5

Delta = distance one wave lags behind another.

Anisotropic minerals > light splits in fast and slow ray > retardation

Question 6

How can we observe the R.I?

Answer 6

By relief => relative contrast.

Doing a Becke Line test

Question 7

How to do a Becke Line test