\ 21 1916 



THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXXIII. — The Several Forms of Calcium Caroonate • 

 by John Johnston, H. E. Meewin, and E. D. Williamson. 



Contents. 



Introduction 



Methods of Identification 



Calotte 



Aragonite 



^-CaCOs 



Other Reputed Forms 



1. Vaterite 



2. Ktypeite 



3. Conchite 



4. Lublinite 



5. "Amorphous" CaCO 3 

 Calcium Carbonate Hexahydrate 

 Tabulated Statement of Experimental Work 

 Solubility of the Several Forms 



Relative Stability of the Several Forms 



Heat of Transformation of Aragonite to Calcite 

 The Precipitation of Unstable Forms 

 Some Applications to the Natural Minerals 

 Recapitulation 



Introduction. 



The prevalence of calcium carbonate as a constituent of the 

 crust of the earth has led to a vast amount of discussion of the 

 chemistry of its formation and of the stability relations of 

 the several crystalline forms in which it occurs. The value, alike 

 to the geologist and to the chemist, of an exact knowledge of 

 the facts has also been repeatedly emphasized. The evidence 

 has, however, been incomplete and in part contradictory or 

 wrongly interpreted, and has never been presented systemat- 

 ically. It appeared, therefore, to be a useful task to give a 

 coherent critical statement of the facts and to discuss the 

 deductions which, in the light of present knowledge, may 



Am. Jour. Sci. — Fourth Series, Vol. XLI, No. 246. — June, 1916. 

 33 



