142 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



color on fresh fracture but was proven to be of normal composition 

 and free from antimony by qualitative tests. Similar crystals have 

 been seen rarely in the Evolution mine near Osburn and in ore from 

 the Pearson antimony mine on Pine Creek, also in specimens of ore 

 from the Liberal King and Casey prospects on Pine Creek. Brilliant 

 silver white crystals occur replacing wall rock in the O. K. mine in 

 Government Gulch and the Corby prospect on Pine Creek and also 

 in the ore of the Hypotheek mine near Kingston in a quartz carbonate 

 gangue with pyrite, chalcopyrite, and tetrahedrite. Some of those 

 from the Hypotheek mine were obtained free by dissolving the 

 carbonate gangue in acid. These were prismatic by vertical elonga- 

 tion, being essentially like Figures 14 to 16. The terminal faces are 

 striated and yield poor measurements which indicate the forms to 

 be s(012) and r(014). The angular values are shown in the following 

 table : 



Forms and angles of simple arsenopyrite crystal from the Hypotheek mine 



Quality, description 



Fair 



....do.... 

 ....do—. 

 ....do.... 



Poor 



Very poor 

 ....do.... 

 ....do.... 



Measured 



55 07 



55 53 



55 34 



56 05 

 53 

 00 

 53 

 00 



90 00 



90 00 



90 00 



90 00 



28 10 



27 15 



14 34 



16 19 



Calculated 



55 46 

 55 46 



00 

 00 



90 00 



90 00 



90 00 



90 00 



30 47 



30 47 



00 ! 16 35 

 00 I 16 35 



The crystals from the Hypotheek mine are frequently twinned on 

 the front dome (101), the commonest twinning law for arsenopyrite. 

 Such a twinned crystal which was measured is shown, projected on 

 the b pinacoid, in Figure 19. The measurements obtained on this 

 crystal are given in the following table: 



Forms and angles of twinned arsenopyrite crystal from the Hypotheek mine 



