Minerals, earth crust

In the previous paragraph, it has been stated that minerals have the same structure but different compositions (phenomenon of isomorphism of minerals) while some minerals have the same composition but different structures (phenomenon of polymorphism of minerals). Mineral composition and structure are both important in studying and classifying minerals. The major class of minerals - based on composition and structure - include elements, sulfides, halides, carbonates, sulfates, oxides, phosphates, and silicates. The silicate class is especially important, because silicon makes up 95% of the minerals, by volume, in the Earth s crust. Mineral classes are divided into families on the basis of the chemicals in each mineral. Families, in turn, are made of groups of minerals that have a similar structure. Groups are further divided into species. 

The outer crust of earth has provided the solid foundation for the evolution of human beings, who are the prime focus of interest and concern to archaeology. The main components of this crust are minerals and rocks, some consolidated and others occurring as sediments, nonconsolidated deposits, created by weathering processes from the minerals and rocks. All these minerals, rocks, and sediments, as well as everything else in the universe, are made up from just over 100 chemical elements listed in Appendix I. Most of the elements in the crust of the earth occur in extremely low relative amounts, and only a few, listed in Table 1, make up almost 99% of its total bulk (Bloom 1969). 

The melting process and the differentiation of the Earth s matter according to its density caused the lighter crust minerals to migrate to the outer layers of the still young Earth, whose surface temperature at that time was such that it was covered by a sea of melted rock (Wills and Bada, 2000). This separation of materials led to the layer structure of the Earth ... 

Some elements in aquatic systems exist only at low concentrations (pg/L range) in spite of readily soluble minerals. This phenomenon is not always caused by a generally small distribution of the concerned element in the earth crust mineral as for instance with uranium. Possible limiting factors are the formation of new minerals, co-precipitation, incongruent solutions, and the formation of solid-solution minerals (i.e. mixed minerals). 

Ono S., Mibe K., and Yoshino T. (2002) Aqueous fluid connectivity in pyrope aggregates water transport into the deep mantle by a subducted oceanic crust without any hydrous minerals. Earth Planet. Sci. Lett. 203, 895-903. 

Arsenic is ubiquitous in nature and is found in detectable concentrations in all environmental matrices. The occurrence of As in the continental crust of Earth is usually given as 1.5 to 2.0 mg/1. The distribution of arsenic in nature is extremely variable, showing little correlation with geological formation, climate, or soil. Numerous minerals, rocks, sediments and soils contain arsenic partly as constituent of sulfide minerals or complex sulfides of metal cations and partly as a constituent retained by soils and/or sediments in occluded or adsorbed forms. The latter is manifested primarily by the adsorption or occlusion of As on hydrous A1 and Fe oxides, but these are not necessarily the only source. Arsenic is also adsorbed on clay colloid, is bound to organic matter and may form slightly water soluble compounds with Al, Fe, Ca and Mg in the soil matrix. Some of the more common minerals in soils are arsenopyrite (FeAsS), Orpiment (AsgSg) etc. 

Application of Mossbauer spectroscopy to crystallography, mineralogy and geology is very similar to chemical applications, with the main emphasis on phase analysis and structure determination. In view of the great importance of iron in the earth s crust and the widespread occurrence of this element in rock-forming minerals, earth scientists have naturally focused attention on applications of - T e Mossbauer spectroscopy. One of the most important groups of rock-forming minerals are the silicates, in which particular lattice position is often occupied by more than two atomic species. In these cases, accurate site occupancy numbers for each species cannot be obtained by diffraction alone. Mossbauer spectroscopy has... 

The alkali metals of Group I are found chiefly as the chlorides (in the earth s crust and in sea water), and also as sulphates and carbonates. Lithium occurs as the aluminatesilicate minerals, spodimene and lepidolite. Of the Group II metals (beryllium to barium) beryllium, the rarest, occurs as the aluminatesilicate, beryl-magnesium is found as the carbonate and (with calcium) as the double carbonate dolomite-, calcium, strontium and barium all occur as carbonates, calcium carbonate being very plentiful as limestone. 

Aluminum can now be produced from clay, but the process is not economically feasible at present. Aluminum is the most abundant metal to be found in the earth s crust (8.1%), but is never found free in nature. In addition to the minerals mentioned above, it is found in granite and in many other common minerals. 

Silicon makes up 25.7% of the earth s crust, by weight, and is the second most abundant element, being exceeded only by oxygen. Silicon is not found free in nature, but occurs chiefly as the oxide and as silicates. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, hornblende, asbestos, feldspar, clay, mica, etc. are but a few of the numerous silicate minerals. 

The metal is the seventh most abundant and makes up about 2.4% by weight of the earth s crust. Most potassium minerals are insoluble and the metal is obtained from them only with great difficulty. 

The element is much more abundant than was thought several years ago. It is now considered to be the 16th most abundant element in the earth s crust. Rubidium occurs in pollucite, leucite, and zinnwaldite, which contains traces up to 1%, in the form of the oxide. It is found in lepidolite to the extent of about 1.5%, and is recovered commercially from this source. Potassium minerals, such as those found at Searles Lake, California, and potassium chloride recovered from the brines in Michigan also contain the element and are commercial sources. It is also found along with cesium in the extensive deposits of pollucite at Bernic Lake, Manitoba. 

Rhenium does not occur free in nature or as a compound in a distinct mineral species. It is, however, widely spread throughout the earth s crust to the extent of about 0.001 ppm. Commercial rhenium in the U.S. today is obtained from molybdenum roaster-flue dusts obtained from copper-sulfide ores mined in the vicinity of Miami, Arizona, and elsewhere in Arizona and Utah. 

The metal is a source of nuclear power. There is probably more energy available for use from thorium in the minerals of the earth s crust than from both uranium and fossil fuels. Any sizable demand from thorium as a nuclear fuel is still several years in the future. Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the HTGR (high-temperature gas-cooled reactor) and MSRE (molten salt converter reactor experiment), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties. 

Oxygen occurs free in air in which it forms 21% by volume. It is also found combined with hydrogen in water and constitutes 86% of the oceans, and with other elements such as minerals constituting ca 50% of the earth s crust. In the laboratory it is usually prepared by the thermal decomposition of potassium chlorate in the presence of manganese dioxide catalyst ... 

The seventh element in order of abundance in the Earth s crust is potassium - about the same as sfjdium with similar properties. While sodium is readily available from the ocean, potassium is found and extracted from many mineral formations. About 90 percent of the potassium that is extracted goes to the production of fertilizers. Other purposes for it are ceramics and fire extinguishers for which potassium bicarbonate is better than sodium bicarbonate. 

Synthetic cryolite solved the supply problem, but synthetic cryolite requires fluorine which is actually more abundant in the Earth s crust than chlorine, but dispersed in small concentrations in rocks. Until the 1960s, fluorspar (CaFj) a mineral long known and used as a flux in various metallurgical operations was the source. A source is phosphate rock that contains fluorine i.s 3% quantity,... 

The structural complexity of the 3D framework aluminosilicates precludes a detailed treatment here, but many of the minerals are of paramount importance. The group includes the feldspars (which are the most abundant of all minerals, and comprise 60% of the earth s crust), the zeolites (which find major applications as molecular sieves, desiccants, ion exchangers and water softeners), and the ultramarines which, as their name implies, often have an intense blue colour. All are constructed from Si04 units in which each O atom is shared by 2 tetrahedra (as in the various forms of Si02 itself), but up to one-half of the Si... 

None of the three elements is particularly abundant in the earth s crust though several minerals contain them as major constituents. As can be seen from Table 13.1, arsenic occurs about halfway down the elements in order of abundance, grouped with several others near 2 ppm. Antimony has only one-tenth of this abundance and Bi, down by a further factor of 20 or more, is about as unabundant as several of the commoner platinum metals and gold. In common with all the post-transition-element metals. As, Sb and Bi are chalcophiles, i.e. they occur in association with the chalcogens S, Se and Te rather than as oxides and silicates. 

The average specific gravity of minerals in the earth s crust is taken to be 2.7. The average specific gravity of saltwater is taken to be 1.07. If the average sedimentary rock porosity is assumed to be 10%, then the total theoretical maximum overburden pressure gradient (lb/fp)/ft becomes... 

The metallic element titanium (11) is relatively abundant in nature it accounts for 0.56% of the earth s crust. This number may not seem very impressive until you realize that it exceeds the combined abundances of ten familiar elements H, N, C, P, S, Cl, Cr, Ni, Cu, and Zn. The most important ore of titanium is ilmenite. a mineral commonly found as a deposit of black sand along beaches in the United States, Canada, Australia, and Norway. In ilmenite. titanium is chemically combined with iron and oxygen. The presence of iron makes the ore magnetic. 

More than 90% of the rocks and minerals found in the earth s crust are silicates, which are essentially ionic Typically the anion has a network covalent structure in which Si044-tetrahedra are bonded to one another in one, two, or three dimensions. The structure shown at the left of Figure 9.15 (p. 243), where the anion is a one-dimensional infinite chain, is typical of fibrous minerals such as diopside, CaSi03 - MgSi03. Asbestos has a related structure in which two chains are linked together to form a double strand. 

Niobium and tantalum are rare elements. The content of niobium and of tantalum in the Earth s crust is lxl0"3 and 2x1 O 4 wt. %, respectively [21]. Niobium and tantalum are encountered in nature together, mostly in the form of oxides that are derived from orthoniobic (orthotantalic), metaniobic (metatantalic) and pyroniobic (pyrotantalic) acids. The main minerals are listed in Table 2, which reveals that the most important source of tantalum and niobium is tantalite-columbite, (Fe,Mn)(Nb,Ta)206. 

Aluminum is the most abundant metallic element in the Earth s crust and, after oxygen and silicon, the third most abundant element (see Fig. 14.1). However, the aluminum content in most minerals is low, and the commercial source of aluminum, bauxite, is a hydrated, impure oxide, Al203-xH20, where x can range from 1 to 3. Bauxite ore, which is red from the iron oxides that it contains (Fig. 14.23), is processed to obtain alumina, A1203, in the Bayer process. In this process, the ore is first treated with aqueous sodium hydroxide, which dissolves the amphoteric alumina as the aluminate ion, Al(OH)4 (aq). Carbon dioxide is then bubbled through the solution to remove OH ions as HCO and to convert some of the aluminate ions into aluminum hydroxide, which precipitates. The aluminum hydroxide is removed and dehydrated to the oxide by heating to 1200°C. 

Iron, Fe, the most widely used of all the d-metals, is the most abundant element on Earth and the second most abundant metal in the Earth s crust (after aluminum). Its principal ores are the oxides hematite, Fe203, and magnetite, Fc C)4. The sulfide mineral pyrite, FeS2 (see Fig. 15.11), is widely available, but it is not used in steelmaking because the sulfur is difficult to remove. 

By far the most abundant phosphate mineral is apatite, which accounts for more than 95% of all P in the Earth s crust. The basic composition of apatite is listed in Table 14-2. Apatite exhibits a hexagonal crystal structure with long open channels parallel to the c-axis. In its pure form, F , OH , or Cl occupies sites along this axis to form fluorapatite, hydroxyapatite, or chlor-apatite, respectively. However, because of the "open" nature of the apatite crystal lattice, many minor substitutions are possible and "pure" forms of apatite as depicted by the general formula in Table 14-2 are rarely found. 

In contrast to SCCO2, the conditions required to obtain SCH2O are harsh. In particular the temperature requirement of 374 °C precludes its synthetic utility for most organic compounds. That said, syntheses in sub-critical but high-temperature water are well studied and will be covered in the next section. Since many natural minerals and precious stones were formed in water at high temperature and pressure in the Earth s crust, the synthesis... 

C03-0100. A mineral is a chemical compound found in the Earth s crust. What are the chemical names of the following minerals (a) Ti02 (rutile) (b) PbS (galena) (c) AI2 O3 (bauxite) (d) CaC03... 

Many of the minerals that form the Earth s crust contain oxoanions. Examples of carbonates are CaC03 (limestone) and MgCa (003)3 (dolomite). Barite (BaS04) is a sulfate mineral. An important phosphate is Caj (P04)3 F (apatite). Two silicates are zircon (ZrSi04) and olivine (a mixture of MgSi04 and FeSi04). 

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