Eye of the Mountain

An artifact recovered in Empire of the Clouds by Chika Cho, Setsuko, Ryuchi, and Teernan.

It has been described as a grapefruit sized amethyst, which strangely reflects no light from it's largest cut surface, otherwise known as the table of the 'brilliant round' cut gem.

Later resurfaced with Teernan in Shadow of the Colossus