Calcite magnesium content

Thus, larger solid/water ratios such as are encountered in pore waters of sediments lead to smaller MgC(>3 contents in the equilibrium magnesian calcites although in either case the magnesium content of the solid increases. Wollast and Reinhard-Derie presented data to support the theory from the standpoint of dissolution and some of our results for the precipitation case... 

We observe the opposite trend, expected from the multiphase hypothesis as a higher solid/solution ratio leads to a smaller mole fraction of MgCOg and, consequently, to a lower solubility (and pH) of the solution. In the first run the high Na2C03 added is offset by tne large amount of calcite added. In the dissolution process the magnesium content of the solid decreases and does so to a greater extent for smaller solid/solution ratios. 

Figure 3.15. Infrared absorbance of the O-H bond as a function of the magnesium content in magnesian calcites after drying at 110°C. All samples are biogenic except for two hydrothermally synthesized magnesian calcites indicated by the letter S. (After Mackenzie et al., 1983.)...

Most of the Rotaliina group of foraminifera mineralizes with magnesian calcite. The magnesium content may vary but the c-axes of the crystals are oriented perpendicular to the inside surface of the shell wall. 

Lowenstam H. (1964) Coexisting calcites and aragonites from skeletal carbonates of marine organisms and their strontium and magnesium contents. In Recent Researches in the Fields of Hydrosphere, Atmosphere, and Nuclear Geochemistry (eds. Y. Miyake and T. Koyama). Maruzen, Tokyo, pp. 373-404. 

Certain ocean precipitates incorporate the Mg2+ ion in their makeup. In calcite (CaC03), it has been shown that the magnesium content enhances calcite solubility, which, in turn, slows crystal growth. This raises concerns about increasing the magnesium content of seawater (as from oil production), which can have adverse implications for calcareous marine organisms such as plankton. 

The most important carbonate-secreting organisms in the oceans are foraminifera, cocco-lithophorides, and pteropods. The carbonate tests vary in size, appearance, crystal form (calcite or aragonite), and magnesium content. The solubility depends on the depth (pressure), temperature, and concentration of CO2 besides the crystal form. For example, the pteropods which secrete shells of aragonite undergo dissolution at shallower depths than the coccolithophorides which secrete calcite shells. 

Rasa coal is exceptional because of its high sulfur content, most of which appears to be organic sulfur. The high organic sulfur content is characteristic of marine-influenced bituminous coals. Rasa coal appears to have been formed in a high-pH marine environment where bacteria thrived. This hypothesis is supported by the presence of substantial amounts of both calcite and dolomite in Rasa coal. The calcium- and magnesium-rich environment where Rasa coal formed is expected to have been alkaline. The... 

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