124 



Average 

 value 



r:a = (T02) : (ГОО) = 69° 58' 



n:a = (TOI) : (TOO) = 50° 12' * 



s:a = (201):(T00) = 29° 51' 



п:Ъ = (Toi): (ÔÏO) = 81° 38' 



e:b = (Til): (010) = 56° 16' 



g:b =(ïTl):(0T0) = 47° 1'* 



f:b =(Т11)-(0Г0) = 16° 6' 



Of the above forms Winther, besides a(lOO} and c{00l}, 

 has determined «{lOl} and s(20l)*, the original designation m 

 of this latter face has been replaced by s that it may be used 

 on {lio). The face /г(б10} given by Winther is determ- 

 ined by 



a: h = 10° 49' 



but it is not possible to see from the material in hand, 

 whether it is placed on the right or the left side of the crystal. 

 The values most nearly approaching it, are on the left side 



(100):(бТ0) = 10°34V2' 

 and on the right side: 



(100): (510) = 11°33V4' and (100): (610) = 9° 44V2'. 



As will appear from this it is not possible to determine 

 its indices more exactly. 



Among the faces mentioned above a{lOO} is found in all 

 the crystals, and is generally very well developed; further 

 è(OlO) is also always found often very predominant; c{00l} is 

 always present, but sometimes very narrow being repressed by 

 w{lOl} and r{l02}; the other faces are more rare. 



The habitus of the crystals is otherwise very varying; 

 sometimes they are isodiametric, but they may also be com- 

 pressed in the direction of each of the three pinacoids, or 

 lengthened in that of each of the three axes, as shown by the 

 figures. Transitions are found between all the different forms; 



