Mineral Resources Potential - Geothermal Resources

200 Mineral Resources Potential of Ethiopia
7.1.1 Coal
Coal is a naturally occurring combustible material consisting
primarily of the element carbn, but with Iow percentages of solid,
liquid, and gaseous hydrocarbs)ns and other materials, such as
compounds of nitrogen and sulfur. Coal is usually classified into
the sub-groups known as anthracite, bituminous, lignite, and peat.
The physical, chemical, and other properties of coal vary
considembly from sample to sample.
Coal forms primarily from ancient plant material that
accumulated in surface environments where the complete dscay of
orgaaic matter was prevented, For example, a plant that died in a
swampy area would quickly be covered with water, silt, sand, and
other sediments. These materials prevented the plant debris from
reacting with oxygen and decomposing to carbon dioxide and
water, as would occur under normal circumstances. Instead,
v b i c bacteria (bacteria that do not require oxygen to live)
' . attacked the plant debris and converted it to simpler forms:
primarily pure carbon and simple compounds
hydrogen (hydroarbom). Because of the way it
(along with petroleum and natural gas) is often
fossil fkl. The initial stage of the decay of a
woody material known as paf. In some parts of the world, peat is
still co1Iected from boggy areas and used as a k l. It is not a good
fuel, however, as it burns poorly and with a great deal of smoke.
If peat is allowed to remain in the ground for long periods
of time, it eventually becomes compacted as layers of sediment, as
overburden, collect above it. The additional pressure and heat of
the overburden gradually converts peat into mother form of coal
known as lignite or brown coal. Continued compaction by
overburden then converts lignite into bituminous (or soft) coal and
finally anthracite (or hard) coal. Coal has been formed many times
in the past, but most abundantly during the Carboniferous Age
(hut 300 million years ago) and again during the Upper