144 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



being the pinacoid a(100) and the dome Z(011) with smaller faces of 

 m(110), g{lll), and v(212). The measurements obtained are as 

 follows : 



Forms and angles on danaite from Lemhi County 



A crystal of the danaite which on polished surface appeared pure 

 and homogeneous was analyzed, yielding good results although, after 

 deducting adhering gangue, the sample weighed only 0.1482 gram. 

 The results of this analysis are given in column 1 below while in 

 columns 2 and 3 are given, for comparison, analyses of danaite from 

 the original locality, Franconia, N. H., and from Skutterud, Norway. 18 



Analyses of danaite 



As shown by the analysis the Idaho material is even higher in 

 cobalt than the original material to which the varietal name was 

 given. The mineral contained no trace of nickel as tested with 

 dimethylglyoxime. The blowpipe reactions are the usual ones for 

 arsenopyrite. In the closed tube in the bunsen flame a broad reddish- 

 black ring of arsenic sulphide above a brilliant metallic ring of me- 

 tallic arsenic is obtained. This test serves to distinguish arsenopy- 

 rite from the associated cobaltite, which requires heating over the 

 blast flame to a much higher temperature before these characteristic 

 closed tube rings are formed. In the open tube the danaite gives a 

 copious sublimate of arsenic trioxide and fumes of sulphur dioxide. 

 It is soluble in hot concentrated nitric acid with separation of some 

 sulphur. The solution, after being diluted with water, is faintly 

 pink. 



>' Dana, System of mineralogy, sixth edition, p. 99. 



