CRYSTALLOGRAPHICAL RELATIONSHIP 265 



When formed under the most suitable conditions, the 

 crystals possessed a markedly high lustre ; but usually the 

 lustre was dull and the reflections poor. This may probably 

 be accounted for by the fact that at temperatures above the 

 average room temperature, efflorescence was observed to 

 take place. 



Fig. 15 shows the general habit of the crystals. They 

 belong to the ditetragonal bipyramidal class, and are usually 



FIG. 15 



slightly elongated along the c axis. The form jlOOj is well 

 developed, as is also the form J111J. jllOj is less pronounced, 

 and jlOlj very small, occurring in only a few crystals. The 

 crystals are capped by small faces of jOOlj. Under suitable 

 conditions of growth, large well-formed crystals were always 

 obtained. 



System : Ditetragonal bipyramidal. 



Axial constants : a : c=l : "7556. 



Forms present : JOOlj, JlOOj, jllOj, jlllj, jlOlj. 



2L 



