Resources play a critical role in Elemental. They are needed to construct buildings, cast spells, and generally accomplish anything of note.
Gold is the basic monetary unit in Elemental and is used to purchase units and construct buildings. Gold is produced by increasing population. Each unit of population produces one tenth of a unit of gold (0.10 gold) per turn. Units also require an upkeep of gold every turn. If they do not receive their gold, they may begin to defect. You can also acquire some additional gold from Gold Mines.
Food is required to increase the population cap in your cities. More people allow you to raise your city level and increases your tax income. 1 Unit of food is used per housing unit built. 1 Unit of food is also used for the founding of each new city. If your food supply becomes negative due to the loss of a farm or through the conquest of a city, *all* of your cities receive a large production penalty until your either acquire more food or demolish sufficient housing to stabilize your food supply.
Materials are used in the construction of buildings and equipment. Materials are a generic resource that can come from Clay, Marble, Stone, and Old Growth Forest resource tiles. You can also build Workshops/Labor Pits which each convert 1 gold into one material each turn. Acquiring a material-producing resource tile can save you quite a bit of money.
Metal is used to make metal weapons and armor. Metal is obtained by building mines on Iron Ore and Ventrii Ore. Ventrii provides more metal per turn than Iron does.
Mana is necessary in order to cast spells. Some Sovereigns and Champions have the ability to generate some mana on their own. Mana is also generated by Air, Water, Earth, and Fire Shards once a mana shrine has been built on them. Mana is a global resource shared by all of the magic users in your Kingdom/Empire.
Magic Crystals (not to be confused with Shards) are used in the production of magical equipment for your troops.