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In the process of coal formation, it will affect the quality of the coal produced. When coal gets more dense pressure, it will produce better quality coal. Below is a classification of coal types that need to be known, namely:

1 Lignite Coal
Lignite or also known as brown coal, is the type of coal that has the lowest quality and is also called "young" geological coal because it is located close to the surface of the earth. According to the Lignite Energy Council, 13.5 percent of lignite coal is gasified into synthetic natural gas and 7.5 percent is used to produce ammonia-based fertilizers. And most of this coal is used to produce electricity. Due to the high degree of heavy relativity on the amount of heat, lignite is usually used in the form of coal powder for coal-fired power plants near the mine area.

According to the World Coal Association, there are ten countries that produce brown coal, namely Germany, Indonesia, Russia, Turkey, Australia, the United States, Greece, Poland, the Czech Republic, and Serbia. In 2010, Indonesia jumped to second place with the highest growth in coal production compared to any country. Despite being in a low position, Germany and Indonesia produced more than 160 million tons of lignite (brown coal) in 2010. Each produced more than 200 percent, or more than double the lignite output compared to other countries in the world.

2.Sub-bituminous Coal
Sub-bituminous is a type of medium coal which is located between the lignite type and the bituminous type. Physically has the characteristics of dark brown tend to be black or dull. Sub-bituminous has a moisture content of 15% to 30% (lower than the type of lignite) based on weight and non-coke (slightly swollen during heating). This coal is suitable for fueling steam power plants.

Sub-bituminous coal has a heat content between 83.00 to 11,500 BTu / lb or 19.3 to 26.7 M J / kg. Its relatively low density and has highwater content make some types of sub-bituminous coal vulnerable to spontaneous combustion if the coal is not packed densely during storage to exclude free air flow.

3.Bituminous Coal
Bituminous is a type of coal that has a higher quality. The majority are black, but sometimes there are still dark brown. Named bituminous because of the content of bitumen / asphalt. This type of coal has a carbon content of 60% to 80%, and the rest is in the form of water, air, hydrogen, and sulfur. Bituminous coal extraction requires the highest safety procedures and involves careful gas monitoring, proper ventilation and alert site management.

4.Batubara Anthracite
Anthracite is a type of coal that has the best quality. This type has a carbon content of 92.1% to 98%, so it is shiny black. The use of anthracite coal in steam power plants is included in the types of High Grade and Ultra High Grade coal. However, this coal supply is still very limited, which is only 1% of total coal mining. The coal producing countries are China, Russia, Ukraine, North Korea, Vietnam, United Kingdom, Australia and the United States. Anthracite coal has a fixed carbon content percentage ranging from 86% to 98%.