Dolomites partition coefficients

Experimental studies of the partitioning of sodium into aragonite, calcite, and dolomite have been carried out by White (1977, 1978), who concluded that the mode of substitution was as Na2CC>3 rather than as Na bicarbonate or hydroxide. The behavior of Na+ does not follow that normally described by a simple partition coefficient, but rather coprecipitation is better described by a Freundlich-type adsorption isotherm equation, implying that adsorption is important. 

On a brighter side, the model of Kretz (1982) for the partitioning of cations between calcite and dolomite has shown impressive correlations between observational data and predicted partition coefficients (see Table 3.2). He proposes, based on the earlier work of Jacobsen and Usdowski (1976), that different partition coefficients exist for a trace cation at Mg and Ca sites in dolomite, which are principally influenced by the size differences between the trace cation and calcium or magnesium. He has made a number of predictions of metal ion partition coefficients in dolomite. It will be interesting to see if future work bears them out. 

The many problems that plague partition coefficients in calcite and aragonite (see Chapter 3) probably also are important for dolomite, but comparable experimental data are not available for dolomite at near Earth surface temperatures. Additional complications are likely to arise in dolomite in because of its degree... 

The original serpentinite was altered to antigorite- dolomite, talc, and tremolite, and the hornblende diorite (H,D ) was altered to chlorite with some tremolite. The numbers refer to samples taken along the alteration zone (the distance between samples 1 and 5 was about 2 ft), and the concentration of the Cr (M), Eu (i, or Sm ( ) in each sample is shown normalized to the levels found in unmetamorphosed serpentinite. The theoretical concentration profile for Sm is shown by the dashed line and was calculated assuming similar partition coefficients (mineral/solution) for all of the minerals formed from the serpentinite. 

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