76 



Dr. L. Vegard on 



coordinates for the construction-point of the Si lattice will 

 be (00Z), where 0<l<c. 



To o-et further, we must take into account the distribution 

 of intensities for different spectra. An important fact in 

 this connexion is that the face (001) gives a normal distri- 

 bution of intensities. This fact limits the possible values of 

 <Z to c/4 or c/2. 



The assumption Z = c/4 ? however, leads to consequences in 

 conflict with observations. Thus it cannot explain that the 

 face (101) gives a nearly normal distribution of intensities, 

 and we have as the only possibility : 



I = cj2. 



The arrangement of the Zr and Si atoms is shown in 

 fig. 3. We might also come to this lattice in another way. 

 It might be considered as composed of two lattices of the rock- 

 salt type with points of construction (000) and (a/4, a/4, c/4), 

 corresponding to the diamond type. 



Fig. 3. 



• Zr atoms 

 OS/ -„ — 



From the isomorphism of the three minerals we should 

 •expect the lattices of the metal atoms to be found by sub- 

 stitution of the atoms in the zircon lattice with corresponding 



