(364) 



Angular values: Measured: Calculated: 



a : m = (100) : (210) =* 26^ 10' — 



h: = (010) : (211) =* 67 18 — 



o:??z = (211):(210)=*107 23 



7/^: ^; = (210):(110)= 18 20 18° 20' 



p: 6z=:(lJ0):(0J0)= 45 30 45 30 



(>:m = (211):(2lO)= 72 37 72 37 



o: (>=:(211):(211)= 45 24 45 24 



a: c = (100) : (001) = 80 28 80 1^'U 



o:m = (211):(210)=: 50 21 50 16 



No distinct cleavage was found. The habit is thick-prismatic with 

 elongation along the vertical axis. 



On |100| normal extinction, on |110| obtuse extinction, sym- 

 metrically orientated in regard to the c-axis. The etching figures on 

 /// and a prove the said symmetry. On jlOOj one branch of the 

 dark hyperbola is visible ; the optic axial-plane is {OlOj. 



On account of its two monoclinic forms, the caesium salt must, 

 therefore, be considered as dimorphous. 



V. Thallous-salt : Tl CO, CC{, . HCO, CCl,. 



The analysis gave: 38,37„ Tl ; calculated 38,467„. 



Sp. gr. at 18° 2,822; molecular volume = 187,74. 



Small and also larger, colourless very lustrous crystals of the form 

 of the K-, and (iVi/J-salt. They give sharp reflexes and may be 

 measured very accurately. 



Thallo-Salt. 

 Fig. 5. 



Tetragonal-trapezohedric. 



a:c = l: 0,7672. 



Forms observed: o = |111| large, predominant and yielding almost 

 perfectly shavp images ; m = jllOj, narrow, but always present and 

 brightly reflecting. 



