1. Renewable
1.1. Can replenish to overcome usage and consumption, either through biological reproduction or other naturally reoccurring processes The replacement rate should balance the consumption rate
1.2. Energy sources
1.2.1. Wind
1.2.1.1. Limitations due to space
1.2.2. Water
1.2.2.1. Can cause destruction to environments and ecosystems, especially when a dam is build over a main river
1.2.3. Solar power
1.2.3.1. Expensive
1.2.3.2. Not really reliable
1.2.4. Biomass
1.2.4.1. Organic matter e.g. corn/palm etc, used as fuel
1.2.4.2. Quite clean
1.2.5. Geothermal energy
1.2.5.1. Heat from the earth
1.3. Others
1.3.1. Wood from trees from building
1.3.2. Plants (tea, tobacco, cotton)
1.3.3. Animals (food, wool)
1.3.4. Rocks
1.3.4.1. For building infrastructure
1.3.4.2. Decoration
2. Naturally occuring substances that can be used for economic gain
3. Non-renewable
3.1. Natural resource that cannot be readily replaced by natural means on a level equal to its consumption.
3.2. Used to produce energy
3.2.1. Fossil fuels
3.2.1.1. Coal
3.2.1.1.1. Are extracted from the ground by coal mining, either underground by shaft mining, or at ground level by open pit mining extraction
3.2.1.1.2. Will be depleted very soon, at the rate the world energy demand increases
3.2.1.2. Natural gas
3.2.1.2.1. cleanest fossil fuel
3.2.1.3. Crude oil
3.2.1.3.1. Can be used to generate heat, drive machinery and fuel vehicles and airplanes; used to manufacture chemical products
3.2.2. Shale gas
3.2.2.1. Gas trapped within deposits of shale in the earth
3.2.2.2. Relatively cleaner than fossil fuels due to lower carbon waste
3.2.2.3. Technology used to harvest shale gas is quite developed
3.2.3. Radioactive materials
3.2.3.1. Nuclear
3.2.3.1.1. Radioactive substances such as uranium, radium etc
3.2.3.1.2. Brings about certain amounts of risks
3.2.3.1.3. Takes very long to decompose
3.2.3.1.4. Can produce explosive amounts of energy
3.3. Others
3.3.1. Minerals
3.3.1.1. Metals etc
3.3.1.2. Precious metals can be used for ornaments/decoration