Studies in the Calcite Group. 



237 



« s- 



Fig. 4. 



It is seen that for the change from 100 per cent to a little under 

 90 per cent of CaMg(C03)o, the molecular volumes occur close 

 to a horizontal line from this point and are spaced, nearly in 

 equal degree, above and below it. But at the point of approxi- 

 mately 88 per cent CaMg(C03)2 there is an increase in the 

 molecular volumes which continues for the remainder of the 

 series. 



