Sulphur

Sulphur was an element.

In 1666, a number of villagers were burning sulphur in a forest where the Doctor's TARDIS landed. (DW: The Visitation)

The planet of the Gonds had an atmosphere that was high in both sulphur and ozone. (DW: The Krotons)

The Eighth Doctor used a sulphur-match to start a fire on the House of Zarn. (EDA: The Eight Doctors)