212 



predominant and yielding good reflexes; o=ijlOTl| [100], positive 

 rliombohedron of (lie first kind, well reflecting, but in most cases 

 only with rather small facets; .i'^|1101| [212], a negative rliombo- 

 hedron of the first kind, commonly much broader than o, somewhat 

 less lustrous; v = |2lri| [421], a negative trigonal bipyramid, about 

 as large as .r, but much smaller than P, commonly yielding good 

 mirror-images; ?■= {11 02|, as a narrow obtusion of the edges of the 

 rhombohedron o, ordinarily absent, but in the other case very lustrous. 

 Sometimes a very narrow and rudimentarily developed prism 

 7?iz={1120| was observed, truncating the basal edges of P. The 

 crystals are mostly very legularly developed as flat trigonal bipyramids; 

 but occasionally more or less deformed, table-shaped individuals are 

 met with, showing the same combination of forms. The faces of P 

 are often striated parallel to the edges P : o. (Fig. 3). Also crystals 

 are found, where o is about twice as lai-ge as P; in this case the 

 striation on P was observed in all cases. 



Finally we met with individuals showing only P and o in about 

 equal size, P having its characteristic striation ; besides them also 

 y was found occasionally, but very small and subordinate, especially 

 in the case of the dextrogyrate component. 



Angular Values : 



P:P" = (1122):(1212)=* 



P.P' = (11 2 2): (11 2 2) = 



P:0 =(1122):(10Tl) = 



X:0 =(1101): (1011) = 



x:y =(1101): (21 11) = 



y.O =(2lTl):(1011) = 



P:0 =(12 12): (1011) = 



0:0 =(10Tl):(0ril) = 



0:r =(1011):(lT02) = 



m:P =(11 20): (11 2 2) = 



No distinct cleavage was observed. 



Optically uniaxial, without noticeable circular polarisation. The 

 character of the birefringence is negative. 



The specific gravity of the crystals at 20° C. was: 2,734; the 

 molecular volume is therefore: 217,77, and the topical parameters 

 are: /: to = 7,0618 : 6.7230, if calculated with respect to hexagonal 

 axes, and ■/ = if' = to = 6,1321, with respect to rhombohedral axes. 



