Coal is a kind of combustible sedimentary rock, comprising the main component that is carbon compound of not less than 50% by weight or 70% by quantity. Coal begins from naturally changing in the plant matters decomposing and accumulating in the basin or swamp for hundred million years ago. At the time the crust of the Earth changes such as earthquake, erupting volcano, or more accumulating sediment. The sedimentary deposits therefore are more affected by pressure and heat under the World. This humus becomes the various kinds of coals.

Origin of Coal
       Coal originates from the plant remains accumulating in the large shallow lakes/seas and afterwards the Earth's crust collapses and the sediment heaps up for millions years. Until that plant remains become the coal jointly resulted by chemical change and geothermal energy. This likes the charcoal making process at present which the firewood is burned in the anaerobic or non-oxygen space. The charcoal is produced instead of burning out to be carbon dioxide.
       Coal is the large reserve of fossil fuel. Coal source spreads aboard the World in many countries. Therefore the coal is the high-stable fuel that results in its more low-priced than other fuels especially natural gas and fuel oil.        American Society for Testing and Material (ASTM) has divided the coal in 4 types/levels aligning from the most to the least compound of carbon i.e. Anthracite, Bituminous, Sub-bituminous, and Lignite. The general properties of coal ranking the high level are the high quantity of carbon, high-heating, and low hydrogen and oxygen. Meanwhile the coal ranking the low level is of the low quantity of carbon, but high hydrogen and oxygen. Each level is subdivided according to the different chemical properties and Calorific Value. Each type of coal has the main properties according to the Table below:

Coal Utilization
       Coal is utilized rather widely from several hundred years to the present due to its sources spread aboard the World and is of the large quantity. Coal utilization was very popular after the Industrial Revolution in English. In 1973, much more popular than before, the oil price shock occurred and resulted in the coal was more used as fuel instead of oil, both for electricity production and industries.

Coal as Fuel
       Coal is regarded as the power source inferior to the petroleum oil and natural gas. The countries possessing the coal source should be deemed that they are highly stable in energy such Indonesia, Russia, China, Germany, and Australia, etc. As a result of alternative energy source other than oil or natural gas that are increasingly, highly-priced.
       Coal is mainly utilized as fuel for electricity production and industries such as steel, cement, lime, and others. It will be less investment than the direct electricity usage. In general, it will be fuel for activities such as water boiling to send the steam to spin the turbine of electricity production or sent the steam to bake such as rubber baking or wood baking, etc.
       Other than the direct combustion, the coal can be converted to be other fuel forms through the coal liquefaction or coal gasification. Coal is utilized as clean fuel in order to reduce the pollution from utilizing the coal as fuel. Under the coal conversion process, acidic or toxic gas can be separated. By-product substances obtained from coal can be utilized in other ways such as sulfur used for sulfuric acid and gypsum production, ammonia used as fertilizer for agriculture, coal ash used for building material production, etc.
       Coal can, other than the fuel benefit, be utilized in other activities. For example, Activated Carbon, an odor neutralizer, is used in the water purifier and appliances requiring odor absorbent feature. Carbon Fiber is strong, light material using for making the glider or sport toots e.g. golf grip, badminton racquet, tennis racket, etc.
       The most coal applied in industries is the premium-grade, Sub-bituminous type. This coal is imported from Australia or Indonesia or other sources that stockpiles at the export port of the origin country and at any area not far from the domestic port.
       In situation of continually increasing price of oil and natural gas, it leads to tight-money. Many businesses must close down due to the energy cost is higher than the revenue. Importing, in this condition, the good quality coal from other countries may help balance or secure the energy cost for electricity production and industrial factories. However, the environmental effect control measure on coal utilization shall be clearly specified.