Ice

Ice was frozen water.

On prehistoric Earth, an Ice Warrior spacecraft crashed and was buried in ice. (TV: The Ice Warriors) Circa 3000 BC, Skaldak was frozen in ice at Earth's North Pole. (TV: Cold War)

The Cold was able to manipulate ice and use it as a weapon, and may have existed within ice itself. (PROSE: Time and Relative)

Some planets had caves made of ice. These included Marinus (TV: The Keys of Marinus) and Shabadabadon (AUDIO: Terror Firma). On Arthur's World, Morgaine trapped the Doctor in an ice cave. (TV: Battlefield)

Other planets seemed to be completely covered in ice. These included Calufrax (TV: The Pirate Planet), Ixon (COMIC: The Therovian Quest), Bruhl (PROSE: Justice of the Glacians), Serac (COMIC: The Betrothal of Sontar), an unnamed human colony (PROSE: Cold Fusion) and an unnamed ice planet (TV: The Daleks' Master Plan).

The core of the planet Spiridon was made of ice. (TV: Planet of the Daleks)