MINERAL RESOURCES CAN BE DEFINED AS naturally occurring substances that can be extracted from the Earth and are useful as fuels and raw materials. Coal, oil, and gas – collectively
called fossil fuels – are commonly included in this group, but are not strictly minerals, because they are of organic origin. Coal formation begins when vegetation is buried and partly decomposed to form peat. Overlying sediments compress the peat and transform it into lignite (soft brown coal). As the overlying sediments accumulate, increasing pressure and temperature eventually transform the lignite into bituminous and hard anthracite coals. Oil and gas are usually formed from organic matter that was deposited in marine sediments. Under the effects of heat and pressure, the compressed organic matter undergoes complex chemical changes to form oil and gas. The oil and gas percolate
upwards through water-saturated, permeable rocks and they may rise to the Earth’s surface or accumulate below an impermeable layer of rock that has been folded or faulted to form a trap – an anticline (upfold) trap, for example. Minerals are inorganic substances that may consist of a single chemical element, such as gold, silver, or copper, or combinations of elements. Some minerals are concentrated in mineralization zones in rock associated with crustal movements or volcanic activity. Others may be found in sediments as placer deposits – accumulations of high-density minerals that have been weathered out of rocks, transported, and deposited (on riverbeds, for example).
