Effect of an error on the grain-shape assumption on the calculated optical constants for Fe-rich samples at 10 K and on the resulting MAC. The results are shown for different grain shapes: spherical (dark blue), prolate (thick lines), and oblate (thin lines) with axis ratios, a/b, of 1.2, 1.6, 1.8, 2.2, 2.4, and 2.8. From left to right, the figures show the resulting errors on n, k, and the MAC.