270 



very lustrous, and perfectly transparent crystals. Their shape is 

 very variable, and some of the most frequent forms are reproduced 

 in fig. 2 a — c. The external aspect is often highly unsymmetrical 

 (fig. 2c); in such cases individuals are occasionally met with, which 

 may be looked upon as apparently enantiomorphous. However, their 

 symmetry is most probably holohedral, the present forms therefore 

 only being speciiil and accidental forms of growth. 



The crystals are identical with those studied by Dufet ^); they 

 differ from those oi\\y in aspect, as Dufet's crystals exhibited the 

 form fi = |110| predominant. 



Triclinic - pinacoidal. 



a-.h :c=: 1,0732: 1 : 1,0316. 



A= 92°45i' a= 98°10f 



j5 = 102 ^ /?=: 104 171 



C= 67 24è 7= 66 llf 



Forms obsei'ved: m = \1^0\, very lustrous and predominant; 

 M = jllOj, smaller, but also well reflecting; 6 = {010}, commonly 

 a little broader than (i , io = \]ll\, broad and yielding good reflexes; 

 § = {1121, well developed and very lustrous; y)=i:{lll}, commonly 

 smaller, but rarely also much greater than §, and giving eminent 

 reflexes; c = {001|, commonly very narrow, occasionally somewhat 

 broader; o := jlllj, broad and beautifully reflecting; .i'={lll|, 

 small and lustrous, often absent; /;^|112|, commonly absent, 

 occasionally very narrow, rarely broad; q = \021\, very small, but 

 well measurable. 



Angles: Observed: Calculated: 



m.b =(110): (010)=* 54° 10' — 



m:,u =(110) : (1ÏÓ)=' 93 3 — 



m : '., =(110) : (111) = * 45 24 i/j 



b:o> =(010) : (111)=' 



y.r,, =(tl0) : (111) = ' 



c:b =(001) : (010) = 

 b' : // = (OK)) : (iTO) = 

 m:p =010) : (lTl) = 



r.>:c' =(llï) : (00T) = 

 m:? =(110) : (Tl2) = 



c:y. =(001) : (irO) = 



,«:? =(1ÏÖ) : (ri5) = 



o:c =(111) : (001) = 



m:o =(110) : (111) = 



1) H. Dufet, Bull, de la Soc. Min. 12. 466. (1889); Gf.: E. Leidié, Ann. de 

 Chim. et Phys (6). 17. 307. (1889). 



