Seer Stone (Witchery)

The Seer Stone is a tool from the Witchery mod. This tool allows witches and warlocks to communicate over large distances. They are commonly used to assist in battle or performing rituals, by summoning other members of their coven. You can also use the Seer Stone on a player to reveal whether or not they have a curse. The Seer Stone is created in the Rite of Infusion, using a Happenstance Oil, a Quartz Sphere, and an Obsidian. Sneak-using a Seer Stone will display information about the user in chat, such as familiars, number of witches in a coven, and which curses the player currently has.

Usage
Use the Seer Stone while held to summon a Coven Witch. Start a rite normally while holding the stone to call an entire coven. Use the stone on a player within 3 blocks to determine if they have a curse or not.

The Seer Stone might refer to Ars Magica 2. Operating on a similar principal as the Astral Barrier, the Seer Stone uses an Etherium aura projected through a spell focus to detect certain nearby objects. However it does not block players and mages from passing through, it sends out a signal to activate other traps.