HOBBS MINERALOGY OF WISCONSIN. 



113 



The angles were measured on two crystals with the fol- 

 lowing results: 



The considerable variation from the theory in the meas- 

 urement fo the angle rz is due to the vicinal character of 

 the face z. With this exception the faces gave excellent 

 images of the signal. 



Arsenopyrite in dike rock at Marquette, Green Lake County. 

 This mineral is found as an accessory constituent in a 

 diabasic rock which occurs in a small dike in Marquette, 

 Green Lake county. The locality is on the south side of 

 the hill south of Mr. Ingalls's house and about one and one- 

 fourth miles south-southwest of the village of Marquette. 



FIG. 2. ARSENOPYRITE FROM MARQUETTE. 



The mineral occurs in crystals three to four millimetres 

 across and bounded by the forms u, iPoo (014) and m, ooP, 

 (110) (See Fig. 2). The u faces are as usual striated par- 

 allel to their intersection. The faces are all bright and 

 reflect well, but are too much rounded to admit of measure- 

 ment Heated on charcoal in the oxidizing and reducing 

 flames of the blowpipe, arsenic and sulphur fumes are 



