Studies in the Calcitc Group. 



223 



In the second half of the table tw^o molecular volumes are 

 given for each analysis. In the column headed "Meas./" the 

 volume has been derived from the percentage composition and 

 the measured specific gravity. In the column headed "Calc." 

 the number has been obtained by multiplying the molecular 

 volume of each molecule, as given in the table on page 216, by its 

 corresponding percentage and dividing the sum of these by 100. 

 For the sake of ease in comparison the molecular volume of pure 

 calcite has been assumed to be 100 and the volumes of the various 

 specimens analyzed have been calculated on that scale. It will 

 be noted that the "measured" molecular volumes of the different 

 calcites remain nearly constant, the average departure from the 

 theoretical value of 100 being 0.56. Although the latter anal- 

 yses in the list show somewhat greater divergencies than those 

 given first, the variation is not great and does not seem to be at 

 all regular. If each molecule retained its own structure and 

 molecular volume when it entered into isomorphous replacement, 

 or, what would practically amount to the same thing, if its 



t Determinations made by the writer. 



