IfEMlTROPE AND INTERSECTED CRYSTALS. 89 



Fig. 116. 





and if we suppose the half b d f, partly turned 

 round as in fig. 116, until b is opposite to c, and d 

 opposite to e, a hemitrope crystal would be produced, 

 resembling one of the varieties of the common spi- 

 nelle. 



Fig. 117. 



Again, if we suppose a right prism, whose base is 

 an oblique angled parallelogram, fig. 117, to be cut 

 through its centre and parallel to its lateral planes ; 



Fig. 118. 



and if we then conceive the portion marked a r, 

 turned round until the edges b and c ? again become 

 parallel as in fig. 118, we shall have a form of hemi- 

 trope crystal not of unfrequent occurrence in sulphate 

 of lime. 



These examples are sufficient to illustrate the man- 

 ner in which hemitrope crystals may be conceived to 

 be produced. But we cannot for a moment imagine 



