Do you know which rock burns or melt? All rocks will eventfully burn or melt at high enough temperatures. The rock we are referring to burns at quite low temperatures and provide us with many chemicals. It can be very soft and crumbly or quite hard; it can be shiny or quite dull.
It can burn in its natural state or it can be treated so that it burns without smoke; it is usually black. Of course, the rock is coal! Like oil, coal is often regarded as the mineral, although as you will see, it also has living origins.
Certain parts of the world, such as the bogs of Scotland and Ireland, the American swamps and places Burma are water-logged. Plants that live there do not decay in the normal way when they die.
The bacteria and fungi which break down the plant remain under more normal conditions, cannot live because there is not enough oxygen and certain acid are formed which kill them.
Under these circumstances, jelly-like humus is formed and this soaks into the fragments of wood and bark and so on, to form a material called peat.
Peat is rich in carbon, and the chemical reactions which occur also produce marsh gas or methane which bunts very readily. Methane is the natural gas which is piped into most of your homes.
In more remote places, such as the northwest of Scotland, where peat is still being formed, it that it can be used for fires during the long, cold winter.
As the peat builds up year after year, the water is squeezed out, and then with further burying underclays and sands, it undergoes a change. It becomes more and more compacted and the gasses are pressed out.
It becomes harder and richer in carbon until eventually, it forms a brown coal. It has often been shown in coal fields that the greater the thickness of rock on top of the coal, the higher the carbon content of the coal. Eventually, anthracite results which contain about 95 percent carbon and is a very high quality and expensive coal.
Most of the coal fields throughout the world are to be found in rocks of carboniferous age. About 300 million years ago, dense swampy forests occurred because of the very rich plant life which had by then developed on Earth, and it is the remains of these forests that gives us most of our coal.
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