B. Interference Figures
i. Acute Bisectrix Figures (A. B. or Bxa)
Look at the muscovite flakes and interference
figure (INT. FIG) slides and examine the interference
figure. How many degrees of stage rotation are
required (starting at extinction position) for the
isogyres to leave the field of view or to be apart
from each other? Draw the interference figure you
see for muscovite when the grain is oriented 45
degrees off the extinction position.
Show the location of the optic axes.
ii. Obtuse Bisectrix Figures (O. B. or Bxo)
Next examine the Topaz slide BH-250-38a and 38b and note the degrees of rotation
required for the isogyres to leave the field of view. This two slides are cut
one perpendicurla and one parallel to the C- axis. Because one of them is Bxa
and the other one Bxo. Can you tell which one is which?