“What is the name of the seeing stone that Pippin finds in the wreckage of Isengard?” — Palantir. More precisely, it is the palantír, one of the ancient seeing-stones of Middle-earth. In The Lord of the Rings, the object is thrown from the tower of Orthanc by Gríma Wormtongue after Saruman’s fall and lands among the ruins of Isengard, where Pippin picks it up.
Gandalf quickly recognizes that the dark globe is not an ordinary stone. Saruman had used the Orthanc-stone to communicate with Sauron, who controlled or influenced the connection. Later, while the company is travelling, Pippin’s curiosity leads him to look into it. Sauron sees him and mistakenly assumes that the hobbit may be connected to the One Ring.
The palantíri were created as instruments of long-distance communication and vision, rather than inherently evil objects. Their danger came from how they were used and from the power of those on the other end. Common mix-ups include identifying the object as the Mirror of Galadriel, which is a different magical object, or confusing it with a location such as Orthanc.