75! 



liislrous crvslixls. wliicli show rallier .strong oscillation!? of their 

 aiigiilai' values, es|)eL'ially in the \erlica! zone. fFig. 16). 

 They are rhombic hisp/ieiwidic 



a:/j:r= 1.0572 : 1 : 0.6801. 



0/>se;i've(l Forms: A^zjOlOj. strongly |iretlouiinant ami rather 

 sharply reflecting; (/ = !100|, very narrow or wholly absent, but 

 with some crystals prominent; //; = jriOi, well developed, giving 

 however multiple images; /•=r}l()l; and r/r=}011j, giving very 

 sharp retleetions; {( = |lllj, in most cases broader ami larger than 

 lo^jllij; this last form reflects very well. 



No distinct cleavage was observed. 



The specific gravity of the crystals was pycnometrically determined 



25° 



at 25° ('., and found to be (/ =: 1.881, the molecular volume is 



thus: 285.80, and the topical axes are: x ■ »l' :"* ^ 7.7731 : 7.3526 : 

 5.004. 



