Optical Mineralogy Flashcards
Study of the interaction of light with minerals
Optical Mineralogy
Opaque minerals commonly studied in reflected light
ore microscopy
general application of optical mineralogy is?
to aid in the identification of minerals, either in rock thin sections or individual mineral grains
It has Low power objective (10x) and Bertrand lens is optional
Orthoscopic (Uncrossed)
Properties that can be observed in Orthoscopic
[] Color and Pleochroism
Cleavage
Shape and Form
Relief/ Refractive Index (R.I.
observed w/ plane prolonged light; not always the same as megacopic color
Color
change in color of a mineral in varying degrees as
the stage is rotated due to differences in light absorption &
extraordinary rays generally expressed as a formula
Pleochroism
The ability of a mineral to separate into smaller
particles bounded of faces of possible crystal form.
Cleavage
qualities of cleavage
[] Perfect
Good
Poor
None
Directions of Cleavage
One Direction
Two Directions
Three Directions
Four Directions
Six Directions
All Directions
-can be expressed by using the terms
eubedral subhedral anhedra
Shape and Form
no recognizable crystal form
anhedral
show imperfect but recognizable
crystal form
subhedral
show sharp and clear crystal form
euhedral
degree of visibility of a transparent mineral in an immersion medium
Relief
R.I of Canada balsam
1.53
index of refraction (R.I) of the mineral is Higher than the medium
. HIGH RELEF
-R.I of the mineral is lower than the medium
LOW RELIEF
almost the same with the medium
ZERO RELIEF
varies as the stage is rotated, takes place if one n
mineral is near n balsam, and the other n mineral
CHANGE of RELIEF
the contrast between a mineral and its
surroundings due to difference in refractive index.
Relief
Relief is __________ when the grain has higher refractive index than surroundings
positive
Relief is __________ when the grain has lower refractive index than surroundings
negative
ratio of the velocity of light in a vacuum to its
velocity in the medium
Refractive Index
R.I, constant velocity in all directions
isotropic/ isotropic substances
more than one R.I, light velocities vary with direction
anisotropic
a band or rim of light visible along a grain/crystal boundary in plane-polarized light.
Becke line
It is best seen using the intermediate power lens (or low
power in some cases), on the edge of the grain, with
the diaphragm stopped down a bit
Becke line
Those with uniform physical properties in all direction
Isotropism
