Pyrovile

Pyroviles are a sapient species of mineral-based lifeforms originally hailing from the planet Pyrovilia.

Description
The Pyroviles are about three meters tall humanoids made out of a rough rock crust with a molten magma interior, as visible from the orifices of their faces; and capable of shooting out fire from their mouths. They need a hot dry environment and are immediately killed by liquid water. Despite this, they are known to survive as minuscule particles which, when inhaled by Humans, trigger a biological transformation which slowly turns the Human body into a new Pyrovile.

History
In the time of the Roman empire on Earth, a Pyrovile craft fleeing from their recently destroyed planet crashed on Earth into Mount Vesuvius and disintegrated along with its crew. The still living Pyrovile particles were mixed within the smoke exhaled by the dormant volcano and ended up inhaled by some of the citizens of Pompeii, who started to undergo the slow transformation into rock creatures. Because the Pyroviles gave them the ability to predict the future, the affected ones formed an organized society bent on helping the aliens conquer all humanity, after which they planned to tamper with the Earth ecology to make it more akin to their needs (eliminating the water bodies and increasing the temperature, mostly). The Doctor prevented this by triggering the eruption of Vesuvius, resulting in the destruction of the Pyroviles but also of the city of Pompeii.

After the Daleks stole 24 planets to power their reality bomb, The Doctor realised that the Pyroviles' homeworld of Pyrovilia was among the stolen planets, hence why they came to Pompeii in the first place. However, the Shadow Proclamation disagreed due to Pyrovilia disappearing 2,000 years earlier. As the Adipose breeding planet and the lost moon of Poosh had also disappeared in the past and future respectively from unknown causes, the Doctor realised planets were being stolen from time as well as space. The status of the Pyroviles as a species after the Daleks were destroyed and Pyrovilia returned where it belonged remains unknown.