Natural resources can be either food, materials or sources of energy. Trees, water and chalk are all examples of natural resources than can be used as raw materials in themselves, or to produce other materials. They are all needed to produced paper, for example. Some natural resources that are used as materials in themselves can also be used as sources of energy. Such natural resources include trees, water, coal and crude oil. Uranium, natural gas and wind are examples of natural resources that can only be used as sources of energy. 

Natural resources that are used either as materials or energy sources can be divided into renewable and non-renewable resources. Renewable resources include things like biomass, wind, water and solar radiation. They replenish after they are used or consumed. In contrast, non-renewable resources include things such as metals, minerals, fossil fuels and uranium. They do not replenish after being used, which means that their supplies are limited.

​​The classification of natural resources.

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