What is the primary cause of color in peridot?

The primary cause of color in peridot is iron. Peridot, which is the gem-quality variety of the mineral olivine, typically exhibits a green hue that varies in intensity based on the amount of iron present in its crystal structure. When iron is present in the mineral, it primarily exists in the ferrous (Fe²⁺) state, contributing to the gem's green color.

While other elements like manganese, chromium, and copper can influence the colors of various gemstones, they do not play a significant role in the color of peridot. Manganese may impart pinkish hues in other minerals, chromium is known for contributing green colors to stones like emerald, and copper can impart blue or green colors in other contexts, but for peridot, the presence of iron is the defining factor for its characteristic green coloration.