This page contains content that is considered "level 2 canon" and may be contradicted by the TV series.
The Eternity Chalice is an object that first appeared in "Steven-less!", a short story in Issue 5.
The Eternity Chalice is a golden/yellow chalice with several green gemstones embedded on its sides. It has a thin handle with a circular bottom. The top of it splits into several points.
The Eternity Chalice is stored at the "Altar of Learning". According to Garnet, it is dropped by Amethyst which caused her to be stuck in a cat-like form until the Crystal Gems return it to its original location.