Coal is one of the 31 rare resources. It only becomes visible once a nation has entered the Industrial Age; until then it appears as a rocky patch, as with Oil. It appears as a fissure with lumps of dark coal in and around it.
Like with all rare resources on land, Coal can be gathered by sending a Merchant from the Market to the resource location. Coal provide the following benefits:
The gather rate of rare resources can be increased in various ways, as described in the main article.
The cost reduction affects all unit, building and technology cost, making Coal's bonus a quite powerful one. Amongst other things, it helps reducing cost for Commerce research and the future tech Artificial Intelligence.