We require metals for making machines, sands and gravels for making roads and buildings, sand for making computer chips, limestone and gypsum for making concrete, clays for making ceramics, gold, silver, copper and aluminum for making electric circuits, and diamonds and corundum (sapphire, ruby, emerald) for abrasives and jewelry. A mineral deposit is a volume of rock enriched in one or more materials. In this sense a mineral refers to a useful material, a definition that is different from the way we defined a mineral back in Chapter
Here the word mineral can be any substance that comes from the Earth. Finding and exploiting mineral deposits requires the application of the principles of geology that you have learned throughout this course. Some minerals are used as they are found in the ground, i. e. they require no further processing or very little processing. For example – gemstones, sand, gravel, and salt (halite). Most minerals must be processed before they are used. For example: * Iron is the found in abundance in minerals, but the process of extracting iron from different minerals varies in cost depending on the mineral.
It is least costly to extract the iron from oxide minerals like hematite (Fe2O3), magnetite (Fe3O4), or limonite [Fe(OH)]. Although iron also occurs in olivines, pyroxenes, amphiboles, and biotite, the concentration of iron in these minerals is less, and cost of extraction is increased because strong bonds between iron, silicon, and oxygen must be broken. * Aluminum is the third most abundant mineral in the Earth’s crust. It occurs in the most common minerals of the crust – the feldspars (NaAlSi3O8, KalSi3O8, ; CaAl2Si2O8, but the cost of extracting the Aluminum from these minerals is high.
Thus, deposits containing the mineral gibbsite [Al(OH)3], are usually sought. This explains why recycling of Aluminum is cost effective, since the Aluminum does not have to be separated from oxygen or silicon. Because such things as extraction costs, manpower costs, and energy costs vary with time and from country to country, what constitutes an economically viable deposit of minerals varies considerably in time and place. In general, the higher the concentration of the substance, the more economical it is to mine. Thus we define an ore as a mineral deposit from which one or more valuable substances can be extracted economically.
Extraction of this oil also requires heating the rock and is therefore energy intensive and not currently cost effective Coal Coal is a sedimentary/metanorphic rock produced in swamps where there is a large-scale accumulation of organic matter from plants. As the plants die they accumulate to first become peat. Compaction of the peat due to burial drives off volatile components like water and methane, eventually producing a black- colored organic- rich coal called lignite. Further compaction and heating results in a more carbon- rich coal called bituminous coal.
If the rock becomes metamorphosed, a high grade coal called anthracite is produced. However, if temperatures and pressures become extremely high, all of the carbon is converted to graphite. Graphite will burn only at high temperatures and is therefore not useful as an energy source. Anthracite coal produces the most energy when burned, with less energy produced by bituminous coal and lignite. Coal is found in beds called seams, usually ranging in thickness from 0. 5 to 3m, although some seams reach 30 m. Two major coal producing periods are known in geologic history.
During the Carboniferous and Permian Periods, the continents were apparently located near the equator and covered by shallow seas. This type of environment favored the growth of vegetation and rapid burial to produce coal. Known reserves of coal far exceed those of other fossil fuels, and may be our best bet for an energy source of the future. Still, burning of the lower grades of coal, like lignite and bituminous coal produces large amounts of waste products that pollute the atmosphere. This problem needs to be overcome before we can further exploit this source of energy. Bottom of Form