Ash

Ash was the powder left of something after it had burned.

The Year Without a Summer in 1816 was blamed on volcanic ash, however, the Thirteenth Doctor pondered whether it was really something else which caused it. (TV: The Haunting of Villa Diodati)

The soil of the petrified jungle on Skaro turned to sand and ashes due to radiation. (TV: The Daleks)

Zolfa-Thura was reduced to sand and ashes after a war. (TV: Meglos)

The "snow" that fell in London on Christmas 2006 was actually ash from the remnants of the Sycorax spaceship. (TV: The Christmas Invasion)

The Third Doctor described Earth in the 30th century as "slag, ash, clinker." (TV: The Mutants)