Oblique Illumination Method for determining Relief

2 common ways to do this:

  1. Insert a blank part-way into the accessory slot so that the field of view is partially shadowed.

    If the grain shows a shadow towards the shadow imposed by the blank,
    ngrain < nbalsam and the grain has (-) relief.

    If the grain shows a shadow away from the shadow imposed by the blank,
    ngrain > nbalsam and the grain has (+) relief.

  2. Placing your hand or a piece of paper placed partly across the light source is another way to produce oblique illumination. The results are the same.
[Return to Relief | Lab 1 | Optics ]
since August 6, 1997.
Last Modified:

EOSC 221
Introduction to Petrology