Fumeroles produce sulphur and mineral deposits, Krafla, Iceland.

Chemicals are condensed from the subterranean steam. A fumerole is a steam vent fed by underground water. Here it has formed in the mud. The steam carries hydrogen sulphide ( and other gasses) which, in contact with oxygen, turn into elemental sulphur and sulphur dioxide. Other chemicals are also present. If it is mainly sulfur it is called a solfatares.

The Krafla area is well known as one of the most active volcanic zones in Iceland. Sulphur is a chemical element ( symbol S ) which occurs in two forms but in Iceland, only elemental sulphur is found.