The Earths Crust

Efforts have been made to determine the compositions of both the primitive mantle and depleted materials in the modern mantle. In the approach of Palme and O Neill (2004), the estimated chemistry of the primitive mantle was determined by subtracting the likely elemental concentrations of the Earth s core from results on the bulk chemistry of the Earth. The chemistry of the bulk Earth may be derived from chemical data on Cl chondrite meteorites, spectrographs of the Sun, and/or analyses of upper mantle rocks. Based on the chemical properties of an element, assumptions can be made on how much of the element was likely to have accumulated in the core. On the basis of this approach, Palme and O Neill (2004, 14) concluded that the arsenic concentration of the primitive mantle was 0.066 0.046 mg kg-1 (Table 3.3). 

Basalts and gabbros are the dominant igneous rocks in oceanic crusts. In rare circumstances, the mafic rocks of the oceanic crust (e.g. at the Mid-Atlantic Ridge) contain various arsenic minerals, including 

Andesite (Bowen Island, British Columbia, Canada) 

Basaltic andesites to andesites (subduction zone, Northeastern Japan, 4 samples) 

---

Oxygen is the most abundant element on earth The earths crust is rich in carbonate and sili cate rocks the oceans are almost entirely water and oxygen constitutes almost one fifth of the air we breathe Carbon ranks only fourteenth among the elements in natural abundance but trails only hydro gen and oxygen in its abundance in the human body It IS the chemical properties of carbon that make it uniquely suitable as the raw material forthe building blocks of life Let s find out more about those chemi cal properties... 

Institute of the Earth Crust, SB RAS, Irkutsk, Russia 128 Lermontov St. Irkutsk, 664033, RUSSIA e-mail xray crust.irk.ru... 

It generally means the total amount of gas in the earth crust in such a form that economic exploitation is currently or potentially feasible. 

Elements are mostly classified to their abundance in the earth crust. The most abundant elements are known as bulk elements (H, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca), the others are considered as trace elements, with the exception of Fe. (Geld-macher-von Mallinckrodt and Meissner 1994). 

The primary sources of trace elements in soils are the parent materials from which soils are derived. These parent materials constitute the reserve for trace elements. Concentrations of trace elements in soils are directly dependent upon their abundance in the earth crust. In general, concentrations of most trace elements in global soils are from one third to three times those in the earth s crust. The logarithm ratios of their concentrations in the global soils over the earth s crust are in the range 0.5 (Fig. 2.2). 

The environmental impact of tin is appreciable, as it is one of the three most enriched metals—only lead and tellurium precede—in the atmospheric particular matter, as compared with the abundance of the element in the earth crust (2.2 ppm). Tin releases to the environment can be methylated by aquatic organisms, yielding organometallic species of toxicity comparable to that of methylated mercury5. 

Tin is an essential trace element for animals. It is soft, pliable and colorless and belongs to group IV of the periodic table, and is corrosion-resistant to many media. Tin occurs in nature mostly as the oxide mineral cassiterite and is ubiquitous in the earth crust in an abundance of 2.5 x 10-4% (Clarke s number, 4 x 10 3). It is one of the earliest metals known to mankind, and evidence of its use dates back over 4000 years. The ancients... 

Titanium is the most abundant metal in the earth crust, and is present in excess of 0.62%. It can be found as dioxy titanium and the salts of titanium acids. Titanium is capable of forming complex anions representing simple titanites. It can also be found in association with niobium, silicates, zircon and other minerals. A total of 70 titanium minerals are known, as mixtures with other minerals and also impurities. Only a few of these minerals are of any economic importance. 

Sodium is the sixth most abundant of the Earths elements. Since it is a highly electropositive metal and so reactive with nonmetals, it is not found in its pure elemental form on Earth. Rather, it is found in numerous compounds in relatively abundant quantities. About 2.83% of the Earths crust consists of sodium in compounds. 

Potassium is the eighth most abundant element in the Earths crust, which contains about 2.6% potassium, but not in natural elemental form. Potassium is slightly less abundant than sodium. It is found in almost all solids on Earth, in soil, and in seawater, which contains 380 ppm of potassium in solution. Some of the potassium ores are sylvite, carnallite, and polyha-lite. Ore deposits are found in New Mexico, California, Salt Lake in Utah, Germany, Russia, and Israel. Potassium metal is produced commercially by two processes. One is thermochemical distillation, which uses hot vapors of gaseous NaCl (sodium chloride) and KCl (potassium chloride) the potassium is cooled and drained off as molten potassium, and the sodium chloride is discharged as a slag. The other procedure is an electrolytic process similar to that used to produce hthium and sodium, with the exception that molten potassium chloride (which melts at about 770°C) is used to produce potassium metal at the cathode (see figure 4.1). 

The stable form of Cs-133 is the 48th most abundant element on Earth, but because it is so reactive, it is always in compound form. The Earths crust contains only about 7 ppm of Cs-133. Like the other alkali metals, it is found in mixtures of complex minerals. Its main source is the mineral pollucite (CsAlSi Og). It is also found in lepidohte, a potassium ore. Pollucite is found in Maine, South Dakota, Manitoba, and Elba and primarily in Rhodesia, South Africa. 

Only about one ounce of natural francium exists in the Earths crust. All the other isotopes of francium are artificially produced in very small amounts (just a few atoms at a time) that exist for a few seconds to minutes. 

Calcium is the fifth most abundant element found in the Earths crust. It is not found as a free element, but as calcium compounds (mostly salts and oxides), which are found on all landmasses of the world as limestone, marble, and chalk. Calcium, particularly as the compound calcium chloride (CaCl ), is found in the oceans to the extent of 0.15%. 

Strontium metal is not found in its elemental state in nature. Its salts and oxide compounds constitute only 0.025% of the Earths crust. Strontium is found in Mexico and Spain in the mineral ores of strontianite (SrCO ) and celestite (SrSO ). As these ores are treated with hydrochloric acid (HCl), they produce strontium chloride (SrCy that is then used, along with potassium chloride (KCl), to form a eutectic mixture to reduce the melting point of the SrCl, as a molten electrolyte in a graphite dish-shaped electrolysis apparatus. This process produces Sr cations collected at the cathode, where they acquire electrons to form strontium metal. At the same time, Cl anions give up electrons at the anode and are released as chlorine gas Cl T. 

Radium is the 85th most abundant element found in the Earths crust. Radium is found in the uranium ores pitchblende and chalcolite, which are both very radioactive. Radium metal exists to the extent of only one part to every three million parts of the uranium ore (pitchblende). Only about one gram of radium is found in every seven or eight tons of uranium ore. This scarcity seems to be the reason that only about five pounds of uranium are produced each year in the entire world. Uranium ores are found in the states of Utah, New Mexico, and Colorado in the United States and in Canada, the Czech Republic, Slovakia, Russia, Zaire, and France. 

Although scandium is chemically similar to rare-earths, it no longer is considered to be one of them. Scandium is the 42nd most abundant element found in the Earths crust, making up about 0.0025% of the Earths crust. It is widely distributed at 5 ppm on the Earth. (It is about as abundant as lithium, as listed in group 1.) Scandium is even more prevalent in the sun and several other stars than it is on Earth. 

Chromium is the 21st most common element found in the Earths crust, and chromium oxide (Cr Oj) is the 10th most abundant of the oxide compounds found on Earth. It is not found in a free metallic state. 

Iron is the fourth most abundant element in the Earths crust (about 5%) and is the ninth most abundant element found in the sun and stars in the universe. The core of the Earth is believed to consist of two layers, or spheres, of iron. The inner core is thought to be molten iron and nickel mixture, and the outer core is a transition phase of iron with the molten magma of the Earths mantle. 

Nickel is the 23rd most abundant element found in the Earths crust. It is somewhat plentiful but scattered and makes up one-hundredth of 1% of igneous rocks. Nickel metal is found in meteorites (as are some other elements). It is believed that molten nickel, along with iron, makes up the central sphere that forms the core of the Earth. 

Niobium is the 33rd most abundant element in the Earths crust and is considered rare. It does not exist as a free elemental metal in nature. Rather, it is found primarily in several mineral ores known as columbite (Fe, Mn, Mg, and Nb with Ta) and pyrochlore [(Ca, NaljNbjOg (O, OH, F)]. These ores are found in Canada and Brazil. Niobium and tantalum [(Fe, Mn)(Ta, Nbl Og] are also products from tin mines in Malaysia and Nigeria. Niobium... 

Rhodium is rare, but not as rare as ruthenium. It makes up only 1 part in 20 milhon of the elements found in the Earths crust. Even so, it is considered the 79th most abundant element and is found mixed with platinum ore, and to a lesser extent, it is found with copper and nickel ores. It is found in Siberia, South Africa, and Ontario, Canada. 

Boron is the 38th most abundant element on Earth. It makes up about 0.001% of the Earths crust, or 10 parts per mdhon, which is about the same abundance as lead. It is not found as a free element in nature but rather in the mineral borax, which is a compound of hydrated sodium, hydrogen, and water. Borax is found in salty lakes, dry lake-beds, or alkali soils. Other naturally occurring compounds are either red crystalline or less dense, dark-brown or black powder. 

Aluminum is the third most abundant element found in the Earths crust. It is found in concentrations of 83,200 ppm (parts-per-million) in the crust. Only the nonmetals oxygen and silicon are found in greater abundance. Aluminum oxide (Al Oj) is the fourth most abundant compound found on Earth, with a weight of 69,900 ppm. Another alum-type compound is potassium aluminum sulfate [KA1(S0 )2 12H20]. Although aluminum is not found in its free metalhc state, it is the most widely distributed metal (in compound form) on Earth. Aluminum is also the most abundant element found on the moon. 

Indium is a rather rare metal. It is the 69th most abundant element, which is about as abundant as silver at 0.05 ppm. Although it is widely spread over the Earths crust, it is found in very small concentrations and always combined with other metal ores. It is never found in its natural metallic state. 

Thallium is the 59th most abundant element found in the Earths crust. It is widely distributed over the Earth, but in very low concentrations. It is found in the mineral/ores of crooksite (a copper ore CuThSe), lorandite (TLAsS ), and hutchinsonite (lead ore, PbTl). It is found mainly in the ores of copper, iron, sulfides, and selenium, but not in its elemental metallic state. Significant amounts of thallium are recovered from the flue dust of industrial smokestacks where zinc and lead ores are smelted. 

Carbon is the I4th most abundant element, making up about 0.048% of the Earths crust. It is the sixth most abundant element in the universe, which contains 3.5 atoms of carbon for every atom of silicon. Carbon is a product of the cosmic nuclear process called fusion, through which helium nuclei are burned and fused together to form carbon atoms with the atomic number 12. Only five elements are more abundant in the universe than carbon hydrogen, helium, oxygen, neon, and nitrogen. 

Silicon, in the form of silicon dioxide (SiO ), is the most abundant compound in the Earths crust. As an element, silicon is second to oxygen in its concentration on Earth, yet it is... 

Germanium, the 52nd most abundant element in the Earths crust, is widely distributed, but never found in its natural elemental state. It is always combined with other elements, particularly oxygen. 

Arsenic is the 53rd most abundant element and is widely distributed in the Earths crust. It occurs naturally in several minerals, but high-grade deposits are rare. Most of the minerals and ores that contain arsenic also contain other metals. Some major sources of arsenic are the minerals orpiment, scherbenkobalt, arsenopyrite, niccohte, realgar, gersdorffite, and smaltite. In addition, most sulfide ores of other metals also contain some arsenic. The three major minerals that produce arsenic are realgar (arsenic monosulfide, AsS), orpiment (arsenic trisidfide, ASjSj), and arsenopyrite (iron arsenosulfide, FeAsS). 

Bismuth is the 70th most abundant element, and it is widely spread over the Earths crust, but in very small amounts. There are no major concentrated sources. It occurs both in the free elemental state and in several ores. The major ore, bismuthinite (B S ), is found in South America. 

Oxygen is the third most abundant element in the universe, making up nearly half the mass of the Earths crust and nine-tenths of the total mass of water. Even the mass of our bodies consists of two-thirds oxygen. Oxygen is also the most abundant element in the Earths atmosphere at 20.947% by volume. 

The 10 most common compounds found in the Earths crust are oxides. Sihcone dioxide (SiOj), or common sand, makes up about half of the oxides in the crust. 

Polonium is found only in trace amounts in the Earths crust. In nature it is found in pitchblende (uranium ore) as a decay product of uranium. Because it is so scarce, it is usually artificially produced by bombarding bismuth-209 with neutrons in a nuclear (atomic) reactor, resulting in bismuth-210, which has a half-hfe of five days. Bi-210 subsequently decays into Po-210 through beta decay The reaction for this process is Bi( ) Bi — °Po + (3-. Only small commercial milligram amounts are produced by this procedure. 

Fluorine is the 13th most abundant element on the Earth. It makes up about 0.06% of the Earths crust. Fluorine is widely distributed in many types of rocks and minerals, but never found in its pure form. Fluorine is as plentiful as nitrogen, chlorine, and copper, but less plentiful than aluminum or iron. 

Helium in the Earth is replaced by the decay of radioactive elements in the Earths crust. Alpha decay produces particles f He ) known as alpha particles, which can become helium atoms after they capture two electrons. This new helium works its way to the surface of the Earth and escapes into the atmosphere where, in time, it escapes into space. 

Neodymium is the third most abundant rare-earth element in the Earths crust (24 ppm). It is reactive with moist air and tarnishes in dry air, forming a coating of Nd O, an oxide with a blue tinge that flakes away, leaving bare metal that then will continue to oxidi2e. 

Samarium is the 39th most abundant element in the Earths crust and the fifth in abundance (6.5 ppm) of all the rare-earths. In 1879 samarium was first identified in the mineral samarskite [(Y, Ce U, Fe) (Nb, Ta, Ti )Ojg]. Today, it is mostly produced by the ion-exchange process from monazite sand. Monazite sand contains almost all the rare-earths, 2.8% of which is samarium. It is also found in the minerals gadolmite, cerite, and samarskite in South Africa, South America, Australia, and the southeastern United States. It can be recovered as a byproduct of the fission process in nuclear reactors. 

Gadohnium is the 40th most abundant element on Earth and the sixth most abundant of the rare-earths found in the Earths crust (6.4 ppm). Like many other rare-earths, gadolinium is found in monazite river sand in India and Brazil and the beach sand of Florida as well as in bastnasite ores in southern California. Similar to other rare-earths, gadolinium is recovered from its minerals by the ion-exchange process. It is also produced by nuclear fission in atomic reactors designed to produce electricity. 

---