From Tolkien Gateway
Jeff Reitz - Palantír of Minas Anor

The Anor-stone was the Gondorian palantír kept at Minas Tirith, taking its name from the older title of that city, Minas Anor. It was kept an unused secret by the Ruling Stewards until it was ultimately used by Steward Denethor II to watch his land, and he eventually even challenged Sauron in a battle of wills. Denethor did not become corrupted, but the great effort of will that this required of him led him to age quickly. He was holding the stone when he committed suicide on a funeral pyre, and after this, only people of exceeding power could see in it anything other than two flaming hands.

See also

 Stones of Arnor  † Annúminas-stone (Annúminas) · Elendil's Stone (Elostirion - Valinor) · † Amon Sûl-stone (Amon Sûl - Fornost)
Stones of Gondor   † Master Stone of Osgiliath (Osgiliath) · † Ithil-stone (Minas Ithil - Barad-dûr) · Anor-stone (Minas Tirith) · Orthanc-stone (Orthanc - Minas Tirith)
Other  Master-stone (Tower of Avallonë)