*Coal is a solid but brittle, carbonaceous black sedimentary rock that burns.
*Coal is divided into four classes: lignite, subbituminous, bituminous, and anthracite.
*Of the commonly minable coals, anthracite is the hardest and has the most carbon, giving it a higher heat value.
*Lignite is the softest coal and has the least amount of carbon.
*By definition, coal is a combustible rock containing more than 50 percent by weight carbonaceous material formed from compaction of variously altered plant remains originally derived from peat.
*Coal, a fossil fuel, is the largest source of energy for the generation of electricity worldwide, as well as one of the largest worldwide anthropogenic sources of carbon dioxide releases. Gross carbon dioxide emissions from coal usage are slightly more than those from petroleum and about double the amount from natural gas.
*About 300 million years ago, the earth had dense forests in low-lying wetland areas. Due to natural processes, like flooding, these forests got buried under the soil. As more and more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. For the process to continue, the plant matter was protected from biodegradation and oxidization, usually by mud or acidic water.
*Great deposits of coal, sandstone, shale and limestone are often found together in sequences hundreds of feet thick. The key to large productive coal beds or seams seems to be long periods of time of organic accumulation over a large flat region, followed by a rapid inundation of sand or soil, and with this sequence repeating as often as possible.
*Coal is a sedimentary rock of biochemical origin. It forms from accumulations of organic matter, likely along the edges of shallow seas and lakes or rivers. Flat swampy areas that are episodically flooded are the best candidates for coal formation.

Coal forms from the accumulation of plant debris, usually in a swamp environment. When plant debris dies and falls into the swamp the standing water of the swamp protects it from decay. Swamp waters are usually deficient in oxygen, which would react with the plant debris and cause it to decay. This lack of oxygen allows the plant debris to persist. In addition, insects and other organisms that might consume the plant debris on land do not survive well under water in an oxygen deficient environment.

Anthracite coal is black and shinier than Bituminous coal.
Bituminous coal is mostly black but I can see a few brown spots on it.
There are a lot of different types of coal.

We use coal every day in our lives and it is very important for us to live. We use coal to power electricity and to power other things.