Boron, aluminium, carbon, silicon

1. Boron, aluminium, carbon, silicon

2. Boron (B) Universe: 0.001 ppm (by weight)  Sun: 0.002 ppm (by weight)  Carbonaceous meteorite: 1.6 ppm  Earth's Crust: 950 ppm  Seawater: 4.4 ppm

3. Introduction of boron One of Goldschmidt early study (in 1923) showed that boron was much moreabundant in sedimentary rocks (300 ppm) than in igneousrocks (3 ppm). The large variation in boron concentration ofdifferent rock types is a consequence of three characteristics:its preferential partitioning into melts, its high mobility in theaqueous phase and its strong affinity for clay minerals.

4. Boron in magmatic processes Boron concentrations relatively low in basalts (6-0.1 ppm), and higher in moreevolved rocks such as granites (85 ppm). Partitioning is notthe only cause for high boron concentrations in granites; someS-type granites contain high concentrations because they arederived from boron-rich sedimentary material. The final residualmelt phases often form pegmatites which may contain upto 1360 ppm boron with the boron concentrated within tourmalines which can contain up to 4% boron. The tourmalines appear from pegmatitic to hydrothermal stages. Well-known boron-silicates in basic magmatites are: danburite, datolite, axinite-group minerals.

5. Boron in magmatic processes Submarine igneous rocks that have been hydrothermallyaltered are often altered to clay minerals such as smectite.Adsorption of boron onto these clays can account forelevated boron concentrations in altered basalts. Boron isthus progressively leached from the host-rock in high temperature in geothermal systems. Detail the order in which boron substitutesinto secondary minerals; in decreasing order: biotite, pyroxenes, plagioclase, amphiboles. Boron frequently emanates from volcanic vents. For example,deposits of sassolite - B(OH)3 - commonly occur around thevents of fumaroles. The presence ofsassolite suggests that boron is transported in the vapor phase.

6. Boron in weathering and sedimentary processes The boron content of sedimentary rocks is partly related tothe amount and type of clay minerals present. Clay minerals, such as illite, smectite and montmorillonite incorporate boron from water both by surface adsorption and as structurallybound boron. In contrary, the Al-oxides(hydroxides) and kaolinite-containing clays show lower boron concentrations. Marine sedimentary rocks tend to contain moreboron than fluvial and lacustrine sedimentary rocks, as theseawater interacting with the marine rock contains more boron.

7. Boron in marine environment The amount of boron in marine sediments is greater than the amount of boron in the ocean waters. Marine sediments contain about 100 ppm boron. Seawater contains 4.6 ppm boron, and concentrations do not vary significantly throughout the oceans. Boronis strongly adsorbed onto secondary minerals (e.g. clay minerals),and these may buffer the seawater boron concentration.Seawater is the source of virtually all of the boron in alteredoceanic crust and much of the boron in sediments and island arc environments.

8. Boron in evaporites The major sourceof boron is inborates from evaporite deposits, most commonly indesert playas, as borax and colemanite. Borax is by far the mostsignificant mined source of boron.Thesedepositsareinconnectionwiththermalactivity (boron-bearingthermalwater). Because of thedifferencesofboron-concentrationsoffreshwater and seewater, themarineboratescontainNa-Mg-Kcations, whilefreshwater/lacustrineboratescontainmainlyCa-Mgcations.

10. Boron in the biosphere Boron is essential element of many plants. However, the soil has negative anomaly about boron (except of soil which lies in see-side). Some marine animals show boron enrichment boron (e.g. corals, silica-spongiae). Marine sapropels have higher boron contains, than freshwater sapropels.

11. Aluminium (Al) Universe: 50 ppm (by weight)  Sun: 60 ppm (by weight)  Carbonaceous meteorite: 9300 ppm  Earth's Crust: 82000 ppm  Seawater:   Atlantic surface: 9.7 x 10-4 ppm     Pacific surface: 1.3 x 10-4 ppm    

12. Aluminium in magmatic processes Aluminium is the most abundant metal (8.3%) in the Earth's crust. It is a major constituent ofmany igneous minerals such as feldspars. The Al-concentration shows enrichment from ultrabasic to acidic magmatics. It has low abundance in early magmatic differentiates, except anorthosite (it main mineral is anorthite). Calc-alkaline magmatic rocks contain the most important rock-forming silicates with Al (feldspars, amphiboles, micas, epidote, quartz). There are characteristic Si4+ Al3+ substitution in these silicates. The Al has a range of coordination numbers ( 4, 5 and 6) in solids / silicates.

13. Aluminium in magmatic and metamorphic processes There are other compounds in magmatic and metamorphic processes, than corundum, spinel, topaz, chrysoberyl etc. The latter rather in post-magmatic stage. Some aluminosilicates can be used as indicators of PTconditions in metamorphism: kyanite, andalusite, sillimanite, which are polymorphs.

14. Aluminium in weathering and sedimentary processes Aluminium has a low solubility at Earth's surface. This solubility is pHdependent and increases at low pH or in alkaline solution. Asecond important behavior concerns the increase of solubilityin presence of organic ligands: chelating complexes with oxalicacids are responsible for a net increase of AI solubility. Thataccounts for the mobilization of AI in acid soils and theincrease of AI concentration in natural acid solutions. Disordered aluminosilicates (allophane and imogolite) are frequently described in soils developed on ash parent materials and as stream precipitates in volcanic areas.

15. Aluminium in weathering and sedimentary processes During weathering of crustal rocks, aluminium is accumulated in clay minerals (kaolinite, smectite, illite, vermiculite), or oxyhydroxides: böhmite AIO(OH) and hydroxide gibbsite, Al(OH)3). The type of secondary Al-containing minerals depend on the degree of chemical weathering. Bauxites mainly formed under tropic or subtropic climates. Lateritic bauxites contain mainly gibbsite, however böhmitecan predominate in karstic bauxites. In tropicalsoils (and occassionally bauxites, too) AI may substitute for Fe in goethite and hematite. Diaspore, AIO(OH) and corundum (Al203) are high-temperature phases which are present in metamorphic bauxites.

16. Aluminium in the biosphere Al widespread in all organics, but not essential element. It was detected up to 20 % Al-oxide some ash of plants, and of coal ash. There is a tendency, that low-class animals contain more Al, than high-class animals.

17. Carbon (C) Universe: 5000 ppm (by weight)  Sun: 3000 ppm (by weight)  Carbonaceous meteorite: 15000 ppm  Atmosphere: 350 ppm  Earth's Crust: 480 ppm  Seawater: 23 ppm   

18. Introduction of carbon Unique characteristic: it forms in more compounds than the all element together. High abundance in the Universe, the Sun, and the Earths crust, too. It has siderophil character in meteorites, lithophil in the Earths crust, atmophil in the atmosphere, and biophil in the biosphere. Essential element for the life.

19. Carbon in magmatic and metamorphic processes Prominent carbon-containing natural materials include diamond, the hardest of the minerals, with a three-dimensionalstructure; graphite, often used as a lubricant because its twodimensionalstructure allows planes to slip laterally. Diamond is high-pressure polymorph of carbon, origin from the Earth mantle, and moves to the crusts quick magmatic processes. Graphite is a high-temperature polymorph of carbon, it forms mainly metamorph processes, or it has pegmatitic origin. However, graphite can form on Earth from sedimentary organic carbon subjected to high pressuresat great depths of burial, high temperatures or both.

20. Carbon in magmatic, metamorphic and sedimentary processes Carbon is a constituent of carbonate anion. The simple carbonates (minerals of calcite and aragonite groups) occur in post-magmatic origin (except carbonatites, which are early differentiates), and in sedimentary environments. Carbonate anion can build in silicates structures, e.g. in scapolites, cancrinites. Similar appearance is known in apatite structure, too. A relatively recently-discovered three-dimensional structure group, called fullerenes, forms a near-spherical cage of carbonatoms. The first identified fullerene structure consisted of 60carbon atoms. Fullerenes occur naturally on Earth in somemetamorphic rocks and meteorite impact crater debris.

21. Carbon in weathering and sedimentary processes Carbonate sedimentscomprise a major portion of theEarth's sedimentary rocks. Carbonate rocks consist almost entirely of calcite (CaCO3), which is predominantly biogenicin origin, and dolomite - CaMg(CO3)2 - which is formed bydiagenic alteration of calcite (so-called Mg-metasomatism). Another major type of sedimentaryrock, shale, contains widely varying amounts andtypes of sedimentary organic carbon. The high-carbon end member of sedimentary organic carbon (mixture of carbon-containing compounds) iscoal. Oil-shale has a wide range of carbon content, and may play a major role as an energy source in the future.

22. Organic minerals – carbon in the lithosphere-biosphere interaction Organic minerals are natural organic compounds with both a well-defined chemical composition and crystallographic properties; their occurrences reveal traces of the high concentration of certain organic compounds in natural environments. The organic minerals are divided into two groups: (1) ionic organic minerals, in which organic anions (it can contains carbon) and various cations are held together by ionic bonds, and (2)molecular organic minerals, in which electroneutral organic molecules (mainly carbon-containing) are bonded by weak intermolecular interactions.

23. Organic minerals – carbon in the lithosphere-biosphere ineraction 1) Ionic organic minerals, oxalates, formates, acetates, mellitates, citrates etc. The most widespread are the oxaletes, e.g. whewellite, weddelite. 2) Molecular organic minerals, amides, purines, polycyclic aromatic organic minerals (e.g. kárpátite), alkanes (evenkite). Molecular mixing occurs in molecular organic minerals and leads to molecular solid-solutions. In natural environments, the distinctionbetween inorganic and organic materials is obscure,and thus the interactions between inorganic and organicmaterials are ubiquitous. Lichens and fungi living onmineral surfaces produce organic acids and facilitatethe dissolution of heavy metals such as Cd, Pb etc.

25. Organic minerals Organic minerals are expected to be promising biomarkers inthe detection of life and in the recognition of biologicalactivity in the geological records of extraterrestrial material, such as Mars. If we consider suchproducts of organic–inorganic interactions and livingorganisms as members of the mineral kingdom, wecould make unlimited contributions to many branchesof Earth and planetary sciences.

26. Silicon (Si) Universe: 700 ppm (by weight)  Sun: 900 ppm (by weight)  Carbonaceous meteorite: 1.4 x 105 ppm   Earth's Crust: 2.771 x 105 ppm   Seawater:    Atlantic surface: 0.03 ppm Atlantic deep: 0.82 ppm Pacific surface: 0.03 ppm Pacific deep: 4.09 ppm

27. Silicon in magmatic processes Silica refers to silicon bonded with two oxygen atoms andis one of the solid forms in which silicon is found in the Earths crust. Silicate is silicon complexed with four oxygen atomsin an anionic complex in aqueous solution or is the other solidform in which silicon is found. The small ionic radius of silicon (0.42 A) and ease of 4-way covalentbonding ensures that it is found mainly in tetrahedral coordination.Some substitution of aluminum (ionic radius 0.51 A)occurs causing an accompanying charge imbalance. This is the most often substitution of silicates.

28. Silicon in magmatic processes It is found on the Earth'ssurface in coordination with oxygen as silica or silicate, SiO2or SiO44-, respectively, although it can form octahedrally coordinatedrarely, SiO68-ina few minerals, notably stishovite (SiO2), or in organic chelates. In solution, silicon is present as a monomer or polymer of silicic acid, H4SiO4. Silicon is a major component of most rock-forming mineralsand hence can reach high concentrations in igneous, metamorphic and sedimentary rocks. The ability of silicate tetrahedra to polymerize inthis manner is largely responsible for its importance in rocktypes which form under a wide range of physical and chemical conditions.

29. Silicon in magmatic processes Silica phase relationships are complex and controlled mainlyby the degree of condensation of silicate monomers and theextent of substitution of aluminum for silicon. The classicalBowen reaction series has two branches describing the orderin which the major silicate minerals crystallize from magma asthe temperature of the melt decreases. The Si-concentration of magmas show enrichment from ultrabasic to acidic range (from olivine – pyroxene – feldspar – to quartz).

30. Silica polymorphs There are several polymorphs of silica of which the dominantform is low or -quartz at Earth's surface conditions. Evidence of the occurrence of high or -quartz can befound as -quartz pseudomorphs. Cristobalite is commonlyintergrown with K-feldspar in devitrification textures.Cristobalite and tridymite are observed rarely in cavities ofsiliceous volcanic rocks. Cristobalite and cristobalite-tridymiteintergrowths known as opal-CT are observed in young cherts,volcanic tuffs, and marine rocks as metastable diageneticphases between opal-A, amorphous silica with varyingamounts of water, and the stable phase, -quartz. Coesite andstishovite are observed in high pressure environments such as impact craters.

31. Silica polymorphs The diagenesis of silica in marine rocks is of considerableinterest because of the high organic carbon contents, and hencepetroleum-generating potential, of many highly siliceous sediments,and because of the effect of silica phase on rock propertieswhich then affect the ability of the rock to transmit orstore petroleum. Planktonic marine diatoms and radiolariaextract silicic acid from seawater to build their frustules ortests. The product is highly porous amorphous silica with avariable but high water content (up to 30%) and high surfacearea. This amorphous silica, opal-A, undergoes diagenetic reactionsusually through an intermediate phase, opal-CT, to the thermodynamically stable phase, quartz.

32. Silicon in weathering and sedimentary processes Silicate minerals formed upon the cooling of magma or duringmetamorphic processes react in three ways upon exposure towater and oxygen at Earth surface conditions. Minerals inwhich all or most of the resulting elements are soluble dissolvecongruently. Olivine and pyroxene are examples of this typeof silicate mineral. Minerals in which at least some of theresulting constituents are only slightly soluble weather incongruently.Feldspars are examples of this type of silicate mineral.In particular, minerals containing aluminum tend to weatherincongruently producing clay minerals, the precise type ofwhich depends upon the climate and parent material.

33. Silicon in weathering and sedimentary processes The highly resistant minerals have very lowaqueous solubilities, they are unreactive.Quartz is an example of this type of mineral and it is foundin soil profiles after other minerals have altered or dissolved.In fact, quartz is so highly resistant to both chemical weatheringand mechanical weathering that it is the main constituentof the highly evolved sedimentary rocks, sandstones. Dissolved silica concentrations in surface waters show different values (river water: 6-16 ppm, seewater in surface: under 1 ppm, in subsurface: 4-6 ppm). This range in concentration reflects the reactivity of the phases involved as well asthe effects of other processes such as adsorption.

34. Silicon in weathering and sedimentary processes Quartz is relatively slow to reach equilibrium while amorphous silicadissolves and precipitates quickly. Hence waters are oftengreatly oversaturated with respect to quartz and under tonearly saturated with respect to amorphous silica. The exceptionare thermal springs in which quartz-saturated waters risingrapidly through near surface rocks are emitted on the surface. At this temperature ( ~ 100°C), the solubilities of quartz and amorphous silica are nearly the same. The solubility of silica strongly depends of pH, it easily dissolved in high pH. If the pH values decrease, the silica precipitate again.