Optics of Minerals Flashcards
Represents index of refraction and vibration direction for light passing in any direction through a material
Optical indicatrix
If all IR for all light rays are similarly plotted, the surface of the indicatrix is
Defined
The long axis of the ellipse is parallel to the
Slow ray vibration
The short axis of the
ellipse is parallel to the
Fast ray vibration
Give example of isotropic materials
- Garnet group
- Spinel group
- Glass
- Volcanic glass
In isotropic minerals, light velocity is uniform in
All directions
Birefringence of isotropic minerals
None, isotropic materials are not birefringent.
Isotropic minerals are ___ when the analyser is engaged
Extinct
All three axes are equal in length, and all are perpendicular to one another
Isometric
Anisotropic minerals has how many optic axis
Single optic axis
Which minerals are Unixial? Which are biaxial?
Uniaxial: Hexagonal and Tetragonal
Biaxial: Monoclinic, Triclinic, Orthorombic
The vibration directions of the light rays that produce the two images
Double refraction
Stationary image
Ordinary ray
Rotating image
Extraordinary ray
one row of dots is stationary, the other row rotates with the
Calcite
one ray vibrates at basal planes / parallel to wave front
Ordinary ray
Circular section
Ordinary ray
another ray vibrates at a principal section
Extraordinary ray
Elliptical section
Extraordinary ray
Is the extraordinary ray the slow ray, or the fast ray?
Slow ray
Optically positive minerals: ordinary ray >extraordinary ray
Slow rays
Optically negative minerals: ordinary ray < extraordinary ray
Fast ray
If the optic axis is horizontal at U+ there are
Ordinary and extraordinary rays
If the optic axis is vertical at U+ there is
There is only extraordinary ray
Assuming mineral is U+ and sample is randomly oriented, there are
Ordinary and extraordinary rays
If ω ray vibrates parallel to trace of optic axis, ε ray vibrates _____________ to the ωray
Perpendicular
the ability of a mineral to absorb different wavelengths of transmitted light depending upon its crystallographic orientations
Pleochroism
Dependent on orientation of mineral, or presence of cleavages of mineral grain
Extinction
True or False
If the mineral is randomly oriented and uniaxial positive, intermediate birefringence can be observed.
True
The shape of any section perpendicular to the optic axis is a __________.
Circle
The ___________ _____________ represents the behavior of light and the changes in the index of refraction in any direction through a material.
Optical Indicatrix
Optically positive minerals have
extraordinary rays that are slow rays.
The ideal thickness of minerals used in the Michel-Levy Color Chart is ______ micrometers.
30
Which of the following crystal systems is not biaxial?
tetragonal
hexagonal
triclinic
monoclinic
orthorhombic
Tetragonal and Hexagonal
The angle of the optic axes of a biaxial mineral is called the ________ angle.
2V
True or False
An isotropic mineral is always extinct when the analyser is engaged.
True
Which extinction is often observed in quartz?
Undulose
True or False
Colorless minerals are often pleochroic.
False
4 types of extinction
Symmetrical, Parallel, Inclined, Undulose
