C. FINDING OPTIC AXIS FIGURES IN RANDOMLY ORIENTED MINERALS
I. In most rocks and minerals, the orientation of crystals will be random and you will have to search for one that is oriented properly so you can obtain an interference figure. You will find oriented minerals but the chances are few. Examine one of the quartz (1,2,3,4,5,6) thin sections BH-250-27. Your goal here is to find a grain that will a yield uniaxial figure that is oriented perpendicular to the c-axis similar to BH-250-36. What should you look for?

II. Sketch what you see. How many isochromatic curves are present? How does this relate to what you know about the birefringence of quartz (1,2,3,4,5,6) ?

III. Next examine one of the Calcite slides 88-C5 or 88-C9 and find a grain that yield uniaxial figure oriented perpendicular to the c-axis. What should you look for? Sketch what you see.

Click here to print entire optics lab 7