Alkaline earth metals

1. Alkaline earth metals

2. Beryllium (Be) Universe: 0.001 ppm (by weight)  Sun: 0.0001 ppm (by weight)  Carbonaceous meteorite: 0.03 ppm  Earth's Crust: 2.6 ppm  Seawater: 0.02 ppm

3. Beryllium in magmatic processes In magmatic differentiation it enriches in granite and alkaline magmatic rocks, e.g. nepheline syenite, especially in pegmatitic processes. Small ionic radius (0,34), similar to Si (0,39), and little coordination number (4). Important Be-minerals in pegmatites: beryl, chrysoberyl, phenakite, all silicates. Rare oxide (bromellite), phosphate (berillonite), borate (hambergite), too. Occassionally appears in skarns and hydrothermal ore deposits (e.g. helvite). It can replaces Al or Si in skarn silicates (garnets, vesuvianite etc.). The largest Be-accumulation connect to acidic pyroclastic rock (here the main Be-minerals is bertrandite).

4. Beryllium in weathering and sediments In weathering processes move together with Al, such in clays, bauxites, and recent marine sediments. It can concentrates in coals (high enrichment in coal ash, too), by absorption in organic matter with REE and other elements (Nb, Ge, V, etc). It concentrates in plants in biosphere, too. The salts of beryllium have strong toxicity.

5. Magnesium (Mg) Universe: 600 ppm (by weight)  Sun: 700 ppm (by weight)  Carbonaceous meteorite: 1.2 x 105 ppm   Earth's Crust: 23000 ppm  Seawater: 1200 ppm

6. Magnesium in magmatic processes Magnesium is a highly compatibleelement during mantle melting, and residual mantle ismore magnesian than fertile mantle. Magnesium remains acompatible element during crystallization of magmas becauseolivine, orthopyroxene and/or clinopyroxene are typicalliquidus phases. Hence, Mg is concentrated in the Earth'smantle, while in the crust it is most abundant in the oceaniccrust and the lower continental crust. Magnesium is a minor or traceelement in highly evolved igneous systems, and typical Mgcontents of granites are on the order of 0.2-5.8 mg/g.

7. Magnesium in magmatic processes It appears both simple and complex compounds. It concentrates in ultrabasic-basic magmatites. Characteristic constituent of mafic rock-forming minerals, as forsterite/olivine, Mg/Fe pyroxenes (e.g. enstatite) and amphiboles. Different abundance was detect about calcium-analogue compounds, such fluorite – sellaite or apatite – wagnerite. However, inverse abundance is well-known, see periclase – lime, or brucite – portlandite pairs. Characteristic Mg2+ / Fe2+ substitution in all rock-forming minerals. The Mg dominance in high temperature and in calk-alkaline magmatites. On the other hand, Fe dominance appear in most of oxides (except of spinel). It forms mainly carbonates in post-magmatic processes.

8. Rock-forming Mg-minerals

9. Magnesium in weathering processes and sediments During weathering of rocks, Mg readily dissolves in the weathering solutions and enters to the hydrosphere. Magnesiumis removed from ocean water by carbonate precipitation, buteven so, Mg is a conservative element in seawater. It enriches in marine and freshwater sediments, too. It has similar characteristics than sodium, but differs from calcium. It forms late precipitates (Mg- or Mg-K-salts) in evaporites. Many times it occurs close associates with borates.

10. Magnesium carbonates It very rare forms directly from seewater or freshwater as dolomite. Much more crystallize in long diagenetic processes. The Mg carbonates form from limestone by Mg-metasomatism with Mg-rich solutions. In the order of total crystallization: limestone dolomitic limestone  dolomite  magnesite. There are many substitutions in cation position in these carbonates (e.g. Mg2+,Fe2+, Mn2, Zn2) e.g. at Rudabánya ore deposit and some magnesite localities of Szepes-Gömör Ore Mts., Eastern Slovakia. Mg carbonates (mainly magnesite) crystallize from Mg-rich ultrabasites and metamorphites (e.g. serpentinite) by hydrothermal solutions, too.

11. Dolomitization In high temperature experiments ( <200°C), followingan induction period, dolomitization proceeds rapidly, producingthe metastable phases (high Mg calcite) and calcian dolomite before stoichiometric dolomite is formed. Several hydrothermal and metamorphic dolomites are stoichiometric and ordered. However, sedimentary dolomites exhibit different degrees of ordering and compositional ranges. At low, sedimentary temperatures, the types of natural waters appears to occur are characterized by high supersaturation, high Mg/Ca ratio and elevated CO3- and HCO3 concentrations. The dolomite produced is, however, weakly ordered and calcian. Holocene dolomites are fine-grained, poorly ordered, and may containup to 7-8 mol% CaCO3.

12. Magnesium in biosphere It forms around 10 pH as hydroxide in soils. Common microcomponent in low-class plants. Essential componens of high plants, e.g. in chlorophil. It catalytic effects is well-known in photosynthesis. Important activator of some enzyms, too. Some marine plants, animals (e.g. algae) have high Mg-content. Occassionally determined from skelets of shells and gastropodas. In high-class animals (and the man) common constituent in bones, musculars, and nervous tissues. Mg-containing carbonates and/or phosphates can produce occlusion in venas (e.g. coronary occlusion).

13. Calcium (Ca) Universe: 70 ppm (by weight)  Sun: 70 ppm (by weight)  Carbonaceous meteorite: 11000 ppm  Earth's Crust: 41000 ppm  Seawater: 390 ppm

14. Calcium in magmatic processes Ca-content of the bulk Earth is variously estimated to be 16.2-19.3 mg/g. Mid-ocean ridge basaltstypically contain about 81 mg/g Ca. Calcium becomes a compatibleelement during crystallization of magmas onceplagioclaseand/or clinopyroxenes begin to crystallize, and duringcrustal melting. The Ca contents of typical granites are of theorder of 2-18 mg/g. Calcium is concentrated in the oceanic( ~81 mg/g) and the lower continental (37-67 mg/g) crusts of the Earth.

15. Calcium in magmatic processes Well-known simple and complex compounds both magmatic and metamorphic rocks. Because of ionic radius of Ca very often forms in the structure of silicates (both mafic and felsic silicates). Important Ca silicates: Ca-garnets (grossular, andradite) Ca-pyroxenes (augite, diopside, hedenbergite), Ca-pyroxenoides (wollastonite), Ca-amphiboles (actinolite, tremolite, hornblende-family), epidote-group, Ca-micas, (margarite, clintonite), Ca-plagioclase (anorthite), felspatoids (cancrinite, haüyne), Ca-zeolites (laumontite, scolecite, series of heulandite and chabazite). Special Ca silicates found as characteristic minerals in high temperature skarns (wollastonite, larnite, rankinite etc.).

16. Calcium in magmatic processes Ca has low abundace in early magmatic differenciates, except anorthite (in anorthosite). However, the basic magmatic rocks, one of main mineral is a Ca-rich basic plagioclase. About the half part of Ca crystallize in later differentiates, as Ca-rich pyroxenes, and amphiboles. Other Ca-containing compounds, e.g. oxides are accessoric components (e.g. perovskite, pyrochlor-group), they occur mainly in alkaline magmatics. There are wolframates (scheelite), molibdates (powellite) and especially carbonates (ankerite, dolomite, calcite, aragonite) in post-magmatic origin.

18. Calcium in weathering and sediments During weathering of rocks, Ca readily dissolves in the weathering solutions and enters tothe hydrosphere. The ratio of Ca : Na is lowerinsediments (e.g. inclays) thanmagmaticrocks. Casimilarto Na, becauseitbuildsinclaymineralsinsmallamounts. There is a differentinCa-contentsbetweenseewater and freshwater (lattercontains more Ca, because of quickerweatheringofanorthitethanalbite). Largemasses of Ca-carbonatesformsinsedimentaryenvironment, insomecaseswithevaporites. Latterenvironmentnotonlycarbonates, butCa-sulphates (gypsum, anhydrite) phosphates (apatite-OH, apatite-Cl, apatite-F) forminlargeamounts.

19. Calcium carbonate and the carbonic acid system Calcium carbonate and the carbonic acid system have a majorrole in the geochemistry of sedimentary carbonates which form,dissolve and reprecipitate at the Earth's surface and in theoceans. Karst dissolution, which shapes the landscape of carbonateterrains, the formation of carbonate platforms andatolls, the dissolution of deep-sea sediments, the developmentof porosity in limestones and dolomites and its destruction viaprecipitation of cements in vugs are some of the phenomenadepending on the calcium carbonate and carbonic acid system interactions. It forms chemical (direct precipitates from water), and biological (skeletal parts of organisms) ways.

20. Calcium carbonate polymorphs Calcium carbonatecrystallizes in a variety of polymorphic forms. The twomost common natural polymorphs are calcite (trigonal) and aragonite (orthorhombic). A third polymorph, vaterite(hexagonal) has been found in gallstones, tissues offractured gastropod shells and as rare alteration product. The vaterite is very instable phase.

21. Calcium carbonate polymorphs Under Earth's surface conditions, calcite is the most abundantand thermodynamically stable polymorph ofCaCO3. Aragonite is relatively abundant and it is stable polymorph athigh pressure. But at surface pressure is unstable and should transform to calcite.Nevertheless, aragonite persists in tectonically uplifted blueschistfacies metamorphic rocks, and precipitates both inorganically (e.g. caves) and through biogenic processes to form carbonate platformsediments and cements. Vaterite isalways metastable under sedimentary conditions. Magnesian calcites are an important variety of CaCO3, they are an important componentof the shallow-water marine sediments either as directprecipitates or as components of the skeletal parts of organisms.

22. Strontium (Sr) Universe: 0.04 ppm (by weight)  Sun: 0.05 ppm (by weight)  Carbonaceous meteorite: 8.9 ppm  Earth's Crust: 360 ppm  Seawater: 7.6 ppm   

23. Barium (Ba) Universe: 0.01 ppm (by weight)  Sun: 0.01 ppm (by weight)  Carbonaceous meteorite: 2.8 ppm  Earth's Crust: 500 ppm  Seawater:   Atlantic surface: 4.7 x 10-3 ppm     Atlantic deep: 9.3 x 10-3 ppm     Pacific surface: 4.7 x 10-3 ppm     Pacific deep: 2 x 10-2 ppm

24. Strontium and barium in magmatic processes Theyrarelyformindepententmineralsinmagmaticprocesses (e.g. bariumfeldspars, thecelsian-paracelsian-hyalophan series). Incommonrock-formingmineralsthe Sr2+substitutes Ca2+ (e.g. plagioclases, apatites, pyroxenes), while Ba2+replaces K+ (mainlyinalkalifeldspars, micas). The bariumcontent in magmatic rocksnormally increases with increasingSiO2concentration. Granitic rocks with high Caconcentrationsare generally enriched in barium, and alkaline rocksare usually highly enriched in strontium.

25. Strontium and barium in magmatic processes Low abundaces in pegmatithic and pneumatolithic phases. In contrary, hydrothermal processes they show higher abundances with many independent minerals. Examples of Sr: celestite, strontianite, svanbergite, and Sr-zeolites (brewsterite-Sr, chabazite-Sr). It substitutes Ca most often in calcite, aragonite, and gypsum. Examples of Ba: barite, witherite, Ba-zeolites (brewsterite-Sr, harmotome, phillipsite-harmotome solid solutions, edingtonite). It replaces K in alkali feldspars (e.g. adularia in epithermal ore deposits). High frequency of barite – celestite solid solution in hydrothermal processes (so-called baritocelestite).

26. Strontium in weathering and sedimentary environment After weathering Sr moves more amounts to the hydrosphere, than Ca. In the evaporation it concentrates in gypsum, calcite, anhydrite by substitution, or it forms independent minerals, e.g. celestite. In sedimentary rocks it is predominantly found in carbonate rockscomposed of calcite and/or dolomite. It may alsobe present in carbonate cement. Diageneticand weathering processes may further distribute andre-distribute strontium among the major rock groups. The amount of Sr found in theserocks, depends on the depositional/diagenetic redistributionof Sr with Ca. In contrast, in other sedimentary rocksthe distribution of Sr into feldspars depends on the substitutionwith K.

27. Barium in sedimentary environment In many natural environments, aqueous barium concentrations are controlled primarily by ion exchange and sorption reactions. Also importantin the aqueous geochemistry of barium is the low solubilityof barite. In alkaline systems, the soluble natureof witherite can control barium mobility. It has better absorption characteristics than strontium, so it moves lesser amounts to oceans. The Sr : Ba ratio in magmatic rocks is 0.6, while in the seewater is 260. In sedimentary rocks, barium normally occurs as barite, or in clays, and in feldspars.Barium can accumulates in manganese oxides in soil and ferromanganese nodules in the oceans.

28. Barium and strontium in sedimentary environment and biosphere Celestite and strontianite common sedimentary Sr-minerals, but they occur always in small amounts. Sr in soils: it concentrates high amounts if Ca-content is higher. Occassionally forms mainly as celestite or strontianite. The precipitation of Ba-Sr sulphates are controlled by microorganism, too. Sr (and rare Ba) occurs in small amounts in skelets of organics.