Optics of Minerals

Question 1

Represents index of refraction and vibration direction for light passing in any direction through a material

Answer 1

Optical indicatrix

Question 2

If all IR for all light rays are similarly plotted, the surface of the indicatrix is

Answer 2

Defined

Question 3

The long axis of the ellipse is parallel to the

Answer 3

Slow ray vibration

Question 4

The short axis of the
ellipse is parallel to the

Answer 4

Fast ray vibration

Question 5

Give example of isotropic materials

Answer 5

• Garnet group
• Spinel group
• Glass
• Volcanic glass

Question 6

In isotropic minerals, light velocity is uniform in

Answer 6

All directions

Question 7

Birefringence of isotropic minerals

Answer 7

None, isotropic materials are not birefringent.

Question 8

Isotropic minerals are ___ when the analyser is engaged

Answer 8

Extinct

Question 9

All three axes are equal in length, and all are perpendicular to one another

Answer 9

Isometric

Question 10

Anisotropic minerals has how many optic axis

Answer 10

Single optic axis

Question 11

Which minerals are Unixial? Which are biaxial?

Answer 11

Uniaxial: Hexagonal and Tetragonal

Biaxial: Monoclinic, Triclinic, Orthorombic

Question 12

The vibration directions of the light rays that produce the two images

Answer 12

Double refraction

Question 13

Stationary image

Answer 13

Ordinary ray

Question 14

Rotating image

Answer 14

Extraordinary ray

Question 15

one row of dots is stationary, the other row rotates with the

Answer 15

Calcite

Question 16

one ray vibrates at basal planes / parallel to wave front

Answer 16

Ordinary ray

Question 17

Circular section

Answer 17

Ordinary ray

Question 18

another ray vibrates at a principal section

Answer 18

Extraordinary ray

Question 19

Elliptical section

Answer 19

Extraordinary ray

Question 20

Is the extraordinary ray the slow ray, or the fast ray?

Answer 20

Slow ray

Question 21

Optically positive minerals: ordinary ray >extraordinary ray

Answer 21

Slow rays

Question 22

Optically negative minerals: ordinary ray < extraordinary ray

Answer 22

Fast ray

Question 23

If the optic axis is horizontal at U+ there are

Answer 23

Ordinary and extraordinary rays

Question 24

If the optic axis is vertical at U+ there is

Answer 24

There is only extraordinary ray

Question 25

Assuming mineral is U+ and sample is randomly oriented, there are

Answer 25

Ordinary and extraordinary rays

Question 26

If ω ray vibrates parallel to trace of optic axis, ε ray vibrates _____________ to the ωray

Answer 26

Perpendicular

Question 27

the ability of a mineral to absorb different wavelengths of transmitted light depending upon its crystallographic orientations

Answer 27

Pleochroism

Question 28

Dependent on orientation of mineral, or presence of cleavages of mineral grain

Answer 28

Extinction

Question 29

True or False If the mineral is randomly oriented and uniaxial positive, intermediate birefringence can be observed.

Answer 29

True

Question 30

The shape of any section perpendicular to the optic axis is a __________.

Answer 30

Circle

Question 31

The ___________ _____________ represents the behavior of light and the changes in the index of refraction in any direction through a material.

Answer 31

Optical Indicatrix

Question 32

Optically positive minerals have

Answer 32

extraordinary rays that are slow rays.

Question 33

The ideal thickness of minerals used in the Michel-Levy Color Chart is ______ micrometers.

Answer 33

30

Question 34

Which of the following crystal systems is not biaxial? tetragonal hexagonal triclinic monoclinic orthorhombic

Answer 34

Tetragonal and Hexagonal

Question 35

The angle of the optic axes of a biaxial mineral is called the ________ angle.

Answer 35

2V

Question 36

True or False An isotropic mineral is always extinct when the analyser is engaged.

Answer 36

True

Question 37

Which extinction is often observed in quartz?

Answer 37

Undulose

Question 38

True or False Colorless minerals are often pleochroic.

Answer 38

False

Question 39

4 types of extinction

Answer 39

Symmetrical, Parallel, Inclined, Undulose