56: 



In comieetion willi tlie crystals investigated up to this moment', 

 the coiTesponding pnndpal distances in the direction of the axes, 

 as in the case of anhydrite, may be recorded here ^). 



§ 5. In previous papers we already discussed some crystals of 

 rhombic symmetry, wiiich will be reviewed again in conneclion 

 witi) what is mentioned above. However we will principally discuss 

 in this paper the results, to which our experiments till now have 

 led us, with respect to the following (.'ijslads : an/u/driie, a rirujonite-, 

 zinc-sidpliate; topaz; struvite; /-asparagine and 6V7/(7?»mÉ;. A following 

 communication will then contain the results widi other rhombic 

 crystals, and at the same lime we shall have then an opportunity 

 to draw Ihe attention to .some problems, which are connected with 

 the special choice of these crystals. 



We will begin here with the crystals of the rhowhic-bipijramidal 

 class first '). 



a. Anhydrite (CaSO,). The used an/fyJ/vVf-crystal was from Stass- 

 FURT. It was lustrous and translucid, and evidently quite homogeneous. 

 Parallel to Ihe three directions of cleavage: jlOOj, {Ü10| and jOOlj, 



1) Note that these numbers relate to a projection distance OP = 100 ni.m.; our 

 figures then have also a diameter of 100 m.m. But for the drawings on Plate IV, 

 which are reduced to ^j^ size, all these values need to be also multiplied with 8/4. 



2) The crystals discussed in this paper are supposed to have such a position, that 

 their parameters become : anhydrite: a:b:c = 0.8932 : 1 : ] .0008 ; arragonite: 

 a:b:c — 0.6224 : 1 : 0.7206 ; zinc sulphate : a:h:c = 0.9804 ; 1 : 0.5631 ; topaz : 

 a:h:c = 5285 : 1 : 0.9539 ; struvite : a:b:c = 0.6667 : 1 : 0.9121 ; calamine : 

 a:b:c — 0.7835 ; 1 : 0.4778 ; l-axparagine : a : b : c = 0.4737 : 1 : 8327 ; sodium- 

 ammonium-tartrate -. a:b:c = 0.8233 : 1 : 0.4200; hamberg ite : a:b:c = 0.7988 : 

 1 0.7268. 



