Distribution and composition of Mg-calcite and dolomite in the water and sediments of Lake Balaton

Abstract

Lake Balaton is a large and shallow lake that is of great economic and cultural importance in landlocked Hungary. Even though the lake has been studied extensively in the last century from a large number of scientific aspects, the mineralogy of its sediments has not been fully explored. The mud at the bottom of the lake consists mostly of silt-sized grains of carbonate minerals with compositions between those of calcite (CaCO 3 ) and dolomite CaMg (CO 3 ) 2 . In order to understand the processes of carbonate precipitation and the influence of water budget fluctuations on the mineralogical character of the sediment, we used X-ray powder diffraction to analyze the changes of cell parameters of carbonate minerals in the upper half meter of the sediment. The major carbonate phase is Mg-calcite that shows a distinct reduction in cell parameters from west to east, reflecting an increase of its Mg-content, in parallel with a gradient of dissolved Mg/Ca ratio in the water. Intriguingly, dolomite, the other widespread carbonate phase in the sediment, also shows a change in cell parameters from west to east, with the deviations from values of stoichiometric dolomite being largest in the Eastern Basin of the lake. The similar pattern of cell parameter changes of Mg-calcite and dolomite suggests that ordered dolomite with slightly anomalous, Ca-rich composition also forms in the lake, probably by direct precipitation from the water. In contrast, protodolomite forms within the sediment through diagenetic processes. Based on our X-ray powder diffraction measurements, we propose a model of carbonate mineral formation and transformation in Lake Balaton. Since the Mg/Ca ratio of the water appears to be the major factor in controlling the compositions of carbonate minerals, and this ratio in turn is governed by the amount of water supply, the properties of the precipitating carbonate minerals are affected by the actual level of the lake water.

Remote Sensing of Water Quality Parameters over Lake Balaton by Using Sentinel-3 OLCI

“…This can allow light to reach the bottom near the southern shore in particular. The bottom of the lake is dominated by fine grain size magnesite-bearing calcareous sediments [28]. This can be easily re-suspended under windy weather conditions, resulting in high turbidity.…”

Indications that Amorphous Calcium Carbonates Occur in Pathological Mineralisation—A Urinary Stone from a Guinea Pig

“…To our knowledge, such broad features have not been reported for calcite, which typically tends to exhibit narrow and intense reflections, but it may well be due to nano-calcite. Another possible explanation for this broadening is the accommodation of magnesium ions in the calcite lattice, which can cause significant broadening of the reflections [45,46]. Quantitatively, the observed shift in the (104) reflection of calcite without magnesium substitution (2θ = 29.429 • ) to 2θ ≈ 29.8 • (maximum of the reflection) gives a change in d (104) from 3.0326 Å (calcite) to~3.0 Å, which is consistent with a Mg 2+ content of ca.…”

Carbonate Minerals with Magnesium in Triassic Terebratula Limestone in the Term of Limestone with Magnesium Application as a Sorbent in Desulfurization of Flue Gases

“…On the basis of the results obtained from measurements done by EDS and WDS methods the values of MgCO 3 content were calculated. These values, data from previous studies (Stanienda, 2013a, b) and the application of the Vegard's law which describes the empirical relationship between the crystal lattice parameter of a mixture and its components (Datta Roy & Das, 2000;Jacob et al, 2007;Lambregts & Frank, 2004;Melteig, 2016;Tompa et al, 2014) (Böttcher et al, 1997). The symmetry of high-Mg calcite crystal is rhombohedral with the space group R3 -c (Althoff, 1977;Paquette & Reeder, 1990 (Dollase & Reeder, 1986 In rocks from all members non-carbonate phases were determined (quartz, chalcedony, feldspars, clay minerals, iron oxides and pyrite).…”