Which of the following energy sources is not a type of coal or coal-precursor?

peat

petroleum

lignite

anthracite

Petroleum

Coal is a combustible sedimentary rock that consists of carbon along with other elements such as hydrogen, sulfur, oxygen and nitrogen. There are mainly four types of coals.

1. Anthracite: It is the highest rank of coal. It is hard, brittle and black coal. It exhibit highest carbon content from all other types.It's surface is lustrous.

2. Bituminous: It is a middle rank coal. It is between subbituminous and anthracite. It is most commonly used coal. It appears shiny and smooth in touch.  

3. Subbituminous: It is a coal that is black in color and dull in appearance.  

4. Lignite: It is brown color coal, it is the lowest grade coal and exhibit least concentration of carbon.  

Peat is not actually coal, but it is the precursor of coal. It is a soft organic material produced by the partially decayed plant materials. When it is exposed to high pressure and heat, it becomes coal.  

Petroleum is the energy source which is not coal or precursor of coal. It is a oil that is found under the surface of earth or under the sea bed.  It is produced by the decomposition of the organic matter from the dead animals and plants around million of years ago.  

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