Which element is responsible for the color in both almandine and peridot?

Almandine and peridot derive their colors primarily from the presence of iron within their crystal structures. In almandine, which is a type of garnet, iron is a key component, contributing to its deep red or purplish-red color. The specific oxidation state of iron in almandine can influence the exact shade observed in the gemstone.

Peridot, on the other hand, is an olivine mineral that contains iron as well, specifically in the form of a mixed crystal structure with magnesium. While peridot's characteristic green color is largely due to the presence of iron, the proportions of iron and magnesium can affect the intensity of the green hue.

Thus, iron plays a crucial role in both gemstones: giving almandine its rich red tones and providing peridot with its beautiful green color, making it the correct answer.