Dolomites stoichiometry

Nordeng, S. H. and D. E Sibley, 1994, Dolomite stoichiometry and Ostwald s step rule. Geochimica et Cosmochimica Acta 58, 191-196. 

Figure 7.13. Conceptual model for the relationship between rock composition, openness of system, and dolomite stoichiometry. Shallow formation of dolomite produces less "ideal" dolomite. More open systems tend to produce more complete dolomitization. (After Sperber et al 1984.)...

Sperber C.M., Wilkinson B.H. and Peacor D.R. (1984) Rock composition, dolomite stoichiometry, and rock/water reactions in dolomitic carbonate rocks. J. Geol. 92,609-622. 

Figures 2-4 summarize the currently available information on the stoichiometry and minor or trace element concentration of saddle dolomite in carbonates, sandstones and carbonate-sandstone mixtures. Saddle dolomite shows a variable elemental composition, from near-stoichiometric to calcian dolomite and/or ankerite. The bulk of published major, minor and trace element data on saddle dolomite are based on electron microprobe analyses, although some authors used powder X-ray diffraction analysis to determine the dolomite stoichiometry. Others used spectrometric techniques (e.g. atomic absorption) to analyse for trace elements. We found it difficult to evaluate this published information because some authors report bulk analyses of several crystals, whereas others report intracrystalline elemental variations. Moreover, analyses are often incomplete (e.g. wt% Fe and Mn no data on Ca and Mg) and cannot be directly recalculated in terms of mol%. Further, some authors report a single measurement whereas others list hundreds of data points.

The fuel nitrogen to NH3 conversion values are comparable to and in-line with values reported by VTT, where a slightly smaller scale pressurised fluidised bed is operated (ca. 500 kWth), for experiments with straw, a fuel quite comparable to Miscanthus, see e.g. Kurkela et al. [13]. Using straw with dolomite as additive they found values in the range of 60-71% fuel nitrogen conversion to NH3, at air stoichiometry values between 0.28 and 0.31. 

The stoichiometry of saddle dolomite varies widely, from 48 to 64 mol% CaC03. Most contains... 

Fig. 2. Chart summarizing the stoichiometry of saddle dolomite. The dashed vertical line indicates stoichiometric dolomite. Data from Wojcik et al. (1992) on saddle dolomite and ankerite are plotted in the limestone and sandstone categories, rather than the mixed category (see Table 1). Data published by Searl Fallick (1990) could not be included because of ambiguous data identification.

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