ENERGETICS OF CALCIUM-RICH DOLOMITE

Citation
L. Chai et al., ENERGETICS OF CALCIUM-RICH DOLOMITE, Geochimica et cosmochimica acta, 59(5), 1995, pp. 939-944
Citations number
45
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
00167037
Volume
59
Issue
5
Year of publication
1995
Pages
939 - 944
Database
ISI
SICI code
0016-7037(1995)59:5<939:EOCD>2.0.ZU;2-N
Abstract
The enthalpy of formation of sedimentary Ca-rich dolomite has been det ermined by oxide melt calorimetry. The results show that Ca-rich dolom ite is energetically different from well-ordered stoichiometric dolomi te. The enthalpy of formation from calcite and magnesite becomes stron gly more endothermic with increasing excess Ca content. This supports the idea that the substitution of Ca in the Mg layer of dolomite is en ergetically unfavorable. Ca-rich dolomite is unstable relative to well -ordered stoichiometric dolomite and calcite. The enthalpy behavior fo r excess Ca substitution in dolomite is different from that of Mg subs titution in calcite; the enthalpy change is much larger in magnitude i n dolomite and is more strongly dependent on composition. Differences in cation order as well as the presence of a modulated structure and l ow-symmetry domains in Ca-rich dolomite cannot be discerned from the e nthalpy data. The findings confirm that the growth and occurrence of C a-rich dolomite in sedimentary environments must be attributed to kine tic factors rather than to equilibrium.