some Carbonates of the Calcite Group. 



345 



contributed by the calcium atoms should be of opposite 

 sign to that of carbon and oxygen. 



The calcium and carbon terms in these equations should 

 be interchanged if the positions of these atoms in the unit 

 are the reverse of those assumed here. Otherwise the 

 expressions are the same in the two cases. 



Fig. 13, ~b 



O = R 



• = C 



• = 



In the present instance case (h) can always be ex- 

 pressed in terms of case (g), (u of course being different 

 in the two cases), so that the structure of calcite has been 

 shown to be that of the special case (g) of the space group 



