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BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



trace of nickel when tested with dimethylglyoxime. The closed tube 

 reactions are those of arsenopyrite. One crystal was freed from the 

 inclosing quartz and measured. This gave the angles of arsenopyrite 



Figs. 18-19.— 18, Arsenopyrite. Qray crystal embedded in quartz. Washington Basin district, 

 Custer County. 19, Arsenopyrite. Twinned crystal. Projected on (010). Hypotheek mine, 

 Shoshone County 



and was found to be prismatic by elongation on the a axis. This 

 crystal is illustrated in Figure 18. The forms and angles measured 

 are as follows: 



Measurements of arsenopyrite from Washington Basin 



