74 



tlie cryKlals diawii iii tig'. \7(i, (lic form Gi=|rilj is preduiiiinant ; 

 a}=:|lllj siniiU and narrow, ö = \0W\. narrow but reflecting well, 

 like a = S100|, wliicli fortn is developed about equally to it ; c =: jOOJj 

 iji most eases absent, but rari'l}- present with oidy one single curved 

 and rudimentary face. 



No distinct cleavage could be observed. 



Feebly dichroitic : on jOlOj for vibrations parallel to tlie rï-axis 

 orange-jellow ; for those perpendicular to these, yellow-orange. 



The plane of the optical axis is jOOJ { ; the '/-axis is probably first 

 bisectrix. 



The specific gravity of the crystals was pycnometrically determined to 



25° 



be: (I = 'J. 888; the molecular \(ilume is thus: "284.74. 



Toinotl ixirawrkrs: -/ ; xp : io — 7.7657 : 7.3399 : 4.9955. 



A' VII. Ritcemic Tridliiili'iiedunnine-CobaUi-nilritt'. 



Formula: \Co {Aem),]{NO.X 



Thin, orange-yellow, iu thicker layers orange-brown, hexagonal 

 plates, often showing mutilated faces, and iutei'growths parallel jOOOJj, 

 ,a : III = (lOÏOj : (OnOj — 60° ; „i : c = lOlO) : (0001) = 90°. 



