Crystallization of Parisite. 



537 



dominant (figures 1, 2) ; (2) pyramidal, the dominant forms 

 being rhoinbohedrons of both positive and negative positions, 

 so balanced, that without measurement, the rhombohedral 

 character is not apparent ; (3) pyramidal (corundum habit), 

 showing a series of second order pyramids and the prism, the 

 pinacoid always broad ; rhombohedral planes, when present, 

 slightly modify the basal edges. (Figure 3.) 





3 





~~" c 



U ] H / / / 







_j / 



r I 

 tv \ 



Figs. 1-3. Parisite. 



In all types the rhombohedral character is clearly demon- 

 strable in almost every crystal, sometimes by simple inspection, 

 more often only after study of the distribution of the meas- 

 ured faces in vertical zones. In practically all cases it is safe 

 to assume that the prism, rarely wholly absent, is of the second 

 order, and this was made the basis of the general orientation 

 of the crystals. The determination of the sign of the rhoinbo- 

 hedrons is often difficult and sometimes impossible since many 

 of them occur in both positions. The sei'ies chosen as positive 

 is the more complex, not only as a whole, but on most crystals, 



