Rock
From Tardis Wiki, the free Doctor Who reference
Rock, or stone, was a naturally occurring aggregate of minerals.
Petrification was the process in which organic matter was turned into stone. The hand of Eldrad was petrified (DW: The Hand of Fear) as were Mrs Pritchard and her daughter, Gwendoline, after Light made them so. (DW: Ghost Light)
On the planet P7E, rock was mined for processing. It eventually became an edible substance. (DW: Underworld)
