[■WALLACE] 



STUDY OF DOLOMITIZATION 



145 



proportions of MgCOg present in the solid state. Reasoning based on 

 the law of mass action * must be somewhat modified by the consideration 

 of the solubilities of the solid phases possible. If the premises on which 

 the deductions are based be granted, the conclusions are of some im- 



Figure 4 



portance in connection with dolomitization in general, and with^the 

 transformation of calcareous algae in particular. The diagrams also 

 explain why a slight increase of Mg ions may lead to a very considerable 

 amount of dolomitization. Whether the inference that dolomite and 

 calcite may, in certain instances, both occur as stable phases can be 

 held to explain the occurrence of magnesian limestones, is a matter that 

 will be discussed later. 



ISOMORPHISM OF CALCITE, DOLOMITE, AND MAGNESITE. 



The foregoing is based on the assumption that calcite, dolomite, 

 and magnesite do not form mixed crystals. The second fact emphasized 

 in the investigation referred to in the introductory part of the paper 

 leads us, however, to enquire more closely into the relationships, iso- 

 morphous or otherwise, of the three minerals. A lack of precision on this 

 point has led to a certain amount of haziness in the conception of the 

 problems underlying dolomitization processes. Retger's classical work 

 on the three minerals f was mainly concerned with specific gravity values, 



*Van Hise. A Treatise on Metamorphism, pp. 805, 806. 

 tZeitschr. f. phys. Chem. VI, 230. 



