Optical Mineralogy L1 Flashcards
class notes
what kind of microscopes are used to study optical mineralogy and where are each type used?
types -transmitting light, used for transparent minerals -reflect light, used for opaque minerals (sulfides/oxides (ore minerals)
what are the theories that explain light behavior?
particle theory wave theory
what does wave theory describe?
polarization, reflection, refraction, interference
what is the size of each type of light in the visible spectrum?
red-700nm violet-400nm
what is light affected by?
electrical component of bonds and atoms magnetic component (small effect)
which direction do electrical and magnetic components vibrate?
right angles to each other and right angles to direction of propogation
what are wave fronts?
// surfaces connecting equivalent pts on adjacent waves
what is a wave normal? what angle is it to wave front?
is the direction the wave is moving and is right angle to wave front
what do light rays show?
direction of propogation
how far apart are successive wave fronts?
1 wave length
what are the 4 processes of optical phenomena? discuss them.
SCATTERING-is stronger with tiny particles that interact with radiation
DIFFRACTION-particle diameter is same size or bigger than light wave
REFRACTION-light passes through different mediums which have different densities. extent of a stick bending (ie) is determined by Snells law
REFLECTION-light bounces off surface of two materials (law of reflection)
what processes are present in a rainbow?
refraction, dispersion and reflection of water
what is the difference between isotropic and anisotropic minerals?
minerals are divided by iso and aniso based on transmission through a crystal ISO-transmit in all directions at EQUAL VELOCITY (cubic crystals and glass minerals) ANISO-DIFF LIGHT VELOCITIES which the velocity is determined by the direction it is travelling through the mineral(all other minerals classes)
discuss the interaction between light and matter
INTERFACE OF TWO MATERIALS-some is TRANSMITTED into new material and some is REFLECTED from surface
what is the behavior of light in minerals result from?
interaction of electrical component of light ray with electron clouds of atoms in the mineral
discuss regular reflection
refer to slide
The regular reflection is the reflection of light rays when they meet (fall on) a smooth (uniform) and glistening surface, where the incident light rays are reflected in one direction.
When a beam of parallel light rays is incident on a smooth and plane surface, the reflected rays will also be parallel, and it is called the regular reflection.
The regular reflection takes place when the light rays are incident on a polished smooth surface like a plane mirror, a stainless steel sheet and a thin sheet of aluminum, so, the reflected rays of light move only in a fixed direction.
We are able to see a very clear reflection on the smooth surface, Every light ray is reflected perfectly from the surface and bounces back in a regular way, The reflected image is very clear and sharp.
discuss refraction
refer to slide
the fact or phenomenon of light, radio waves, etc. being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density.
change in direction of propagation of any wave as a result of its traveling at different speeds at different points along the wave front.
measurement of the focusing characteristics of an eye or eyes.
how do we measure the amount a light bends in a material and discuss it
by index of REFRACTION (n)
what does a high index of refraction indicate?
low velocity
discuss Snell’s Law. what is it used for? when is it refracted TOWARDS and AWAY from the normal?
- calculates how the light will bend when entering a new medium -TOWARDS-HIGHER refractive index
- AWAY-LOWER refractive index
discuss total internal REFLECTION
refer to slide
Total internal reflection is the phenomenon which occurs when a propagated wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary and the incident angle is greater than the critical angle, the wave cannot pass through and is entirely reflected. The critical angle is the angle of incidence above which the total internal reflection occurs. This is particularly common as an optical phenomenon, where light waves are involved, but it occurs with many types of waves, such as electromagnetic waves in general or sound waves. When a wave reaches a boundary between different materials at an angle of less than 25° with different refractive indices, the wave will in general be partially refracted at the boundary surface, and partially reflected. However, if the angle of incidence is greater (i.e. the direction of propagation is closer to being parallel to the boundary) than the critical angle – the angle of incidence at which light is refracted such that it travels along the boundary – then the wave will not cross the boundary, but will instead be totally reflected back internally. This can only occur when the wave in a medium with a higher refractive index (n1) reaches a boundary with a medium of lower refractive index (n2). For example, it will occur with light reaching air from glass, but not when reaching glass from air
when is light refracted and not refracted when going from 1-2 (n)?
REFRACTED-n1n2
what is the critical angle?
angle of incidence that produces a refraction of 90 degrees
what happens when the angle of incidence is >CA
no light REFRACTED, it is all REFLECTED (=total internal reflection)
discuss dispersion
refer to slide
discuss diamond cut
refer to slide
why are diamonds shiny. why are some diamonds not shiny?
based on the quality of a diamond cut. when the diamond is well cut the light bounces off the mirror surfaces and REFLECTED back through top (brilliance/fire) brilliance-(reflection) fire-prism effect (dispersion)
tell me what a becke line test is and why is it useful
-it is used to determine the relative indices of refraction (+ vs - relief)
-
The microscope stage is lowered slightly. This throws the mineral out of focus resulting in a white band of light (Becke Line) to be visible along the crystal boundaries.
If the light band moves into the mineral, the mineral has a higher index of refraction than the surrounding medium, and therefore the mineral has positive relief.
If the light band moves into the medium (i.e. away from the mineral), the medium has a higher index of refraction than the mineral, and therefore the mineral has negative relief
https://www.youtube.com/watch?v=O-KALJ3p26Q
what is index of refraction (lab)
what is the beck line test method (lab)
what is pleochroism?
what is cross polars?
