Sulfur

Sulfur is an ore that can be obtained from resource nodes but does not currently serve any purpose. Based on it's description, it will likely be used in the creation of gunpowder.

Obtaining
It can be harvested by hand or by placing a miner on a resource node.

There are currently 11 Sulfur resource nodes in-game; 1 impure, and 10 normal.

Trivia
Traditional gunpowder is composed of Sulfur, Carbon, and Potassium Nitrate. Because of this, it can be speculated that gunpowder will be created by combining coal and sulfur, along with possibly other materials.