Coal is an example of

2:50 AM    Coal , Geology , Rocks , Science , Sedimentary Rocks   

Q. Coal is an example of

1. Igneous rocks
2. Sedimentary rocks
3. Metamorphic rocks
4. None of the above

Answer: Sedimentary Rocks

Coal is an example of Sedimentary Rocks.

Coal is a hard rock that can be burned as a solid fossil fuel. It is mostly carbon but also contains hydrogen, sulfur, oxygen and nitrogen. It is a sedimentary rock formed from peat, by the pressure of rocks laid down later on top.

Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements; chiefly hydrogen, sulfur, oxygen, and nitrogen.

Different kinds of coal and how they form

Layer of bituminous coal at the seaside in Nova Scotia

Under suitable conditions, plant material is transformed step by step into

1. Peat is not yet coal.
2. Lignite (brown coal) is the dirtiest coal, is about 60%-70% carbon, and is used as fuel for electric power generation. Jet is a compact form of lignite that is sometimes polished and has long been used as an ornamental stone.
3. Sub-bituminous coal is used as fuel for steam-electric power generation. Also, it is a source of light aromatic hydrocarbons for the chemical synthesis industry.
4. Bituminous coal is a dense rock, black but sometimes dark brown. It is relatively soft coal that breaks and burns readily and quickly. It used as fuel in power stations, and for heat and power applications in manufacturing, for blacksmithing; and to make coke.
5. Steam coal was once widely used as a fuel for steam locomotives. In this specialized use it is sometimes known as sea-coal in the U.S. Small steam coal (dry small steam nuts or DSSN) was used as a fuel for domestic water heating.
6. Anthracite is a harder, glossy, black coal. It is longer burning and used mainly for residential and commercial space heating.
7. Graphite is difficult to burn and is not so commonly used as fuel. It is still used in pencils, mixed with clay. When powdered, it can be used as a lubricant.

Diamond is commonly believed to be the end result of this process, but this is not true. Diamond is carbon but is not formed from coal.

Coal contains impurities. The particular impurities determine the use. Coking coal has little ash or sulfur or phosphorus. Those would spoil the iron made by the blast furnace.