Coal

There are two types of coal: Lignite and anthracite. The most currently used unit is the Bak (100 kg of coal).
 * Lignite is used like currency: it governs all transactions. Lignite can also be used as fuel. Lignite is referred to as Lignite-money.
 * Anthracite is richer than lignite, and is exclusively used for fuelling steam trains. In general, it's better to focus on using anthracite exclusively to fuel the train, as otherwise you're literally burning money.