OPTICAL MINERALOGY
TRIVIA
ROUND 2!
Round 2 – Question 1
Under cross-polars, when will this
mineral go to extinction?
Round 2 – Question 2
The interference colors shown by
a mineral under cross-polars
depends on the thickness of the
mineral and what else?
Round 2 – Question 3
When a mineral shows nearly black
interference colors, what type of
indicatrix section is in the plane of
the mineral?
Round 2 – Question 4
What type of optic figure is this?
Round 2 – Question 5
What causes the black isogyres
Round 2 – Question 6
What is the optic sign
indicated by this figure?
Round 2 – Question 7
Which two vibration
directions in this
biaxial indicatrix
will display
maximum
birefringence?
Round 2 – Question 8
This is an example
of a negative
biaxial indicatrix.
What is does this
imply about the
relative values of ,
 and ?
Round 2 – Question 9
What type of optic figure is this?
Round 2 – Question 10
If the colors go up in figure C,
what does this imply about the sign
of elongation?
End of Round 2
Pass your answers to the team on your
right for grading.
Round 2 – Question 1
Under cross-polars, when will this mineral go
to extinction?
When the O & E vibration directions are
parallel to the polarizing directions (N-S/E-W)
Round 2 – Question 2
The interference colors shown by
a mineral under cross-polars
depends on the thickness of the
mineral and what else?
birefringence or difference in two
indicies of refraction in section
Round 2 – Question 3
When a mineral shows nearly black
interference colors, what type of
indicatrix section is in the plane of
the mineral?
circular section
Round 2 – Question 4
What type of optic figure is this?
uniaxial optic axis figure
Round 2 – Question 5
What causes the black isogyres
Alignment of two vibration
directions parallel to polarizers
Round 2 – Question 6
What is the optic sign
indicated by this figure?
Positive
Round 2 – Question 7
Which two vibration
directions in this
biaxial indicatrix
will display
maximum
birefringence?
 and 
Round 2 – Question 8
This is an example
of a negative
biaxial indicatrix.
What is does this
imply about the
relative values of ,
 and ?
 is closer to 
than to 
Round 2 – Question 9
What type of optic figure is this?
Acute Bisectrix (Bxa)
Round 2 – Question 10
If the colors go up in figure C,
what does this imply about the sign
of elongation?
Length slow