344 R- W. G. Wyckoff— Crystal Structures of 



When all the indices are odd or two are even and one is 

 odd, this expression reduces to 



A = 



B=2 {sin2 7r^ (k-Jc) + sin 2 it u (l-h) + sin 2 it u {k—l)\. 



When they are two odd and one even : 



A=2C±Oa+20 {cos 2 it u Qi-h) + cos 2 it u (I- h) 



+ COS 2 IT u (k — 1)\. 



B=0. 



Fig. 13, a 



O = R 



• = C 



• = 



Fig. 13. — The arrangement of the atoms in the unit of structure of 

 members of the calcite group, RC0 3 . 



If {h + h + l) is divisible by four, the calcium term should 

 be added to the carbon and oxygen terms ; if on the other 

 hand, this sum can be divided by two only, the emplitude 



