Palache and Wood — Crystallographic Study of Millerite. 355 



Doubtful Forms. 



The following forms, for one reason or another, given in 

 detail under each form, are presented as possibly present on 

 the species, but not as established beyond cavil. 



% (4150). This form was reported by Laspeyres, but not 

 very well established by his measurements. We obtained poor 

 measurements partly confirming it, but the form is still in 

 doubt, neither his measurements nor ours being good enough 

 to certify it. Our measurements follow. 



Crystal. Signal. Reading. 



2 



extremely poor 



18° 52' 



2 



extremely poor 



18° 58' 



2 



poor 



19° 01' 



Average 



very poor 



18° 57' 



Calculated 





19° 06'-4 



The agreement of our measurements with the calculations 

 is better than that of- Laspeyres's measurements, but the faces 

 noted were all on one crystal, and two of them were very 

 doubtful.__ 



f (9'4*13*0). This prism is new and the measurements on 

 which it is based follow. 



Crystal. Signal. Reading. 



1 





fair 12° 26' 



12 



14 

 Average 

 Calculated 





poor 12° 29' 



very good 12° 29' 



fair to good 12° 28' 



12° 31'-2. 



yreement is 



close 



enough to establish the form, 



The agreement is close enough to establish the form, but 

 the faces are few in number, though well distributed. The 

 signals, however, are good, and in the case of crystal 14, at 

 least, the reading corresponds to a definite face of good quality 

 which can be seen in the goniometer. In this respect the face 

 differs from most of the oscillation planes and, moreover, it is 

 placed very close to its computed position. Therefore the 

 form is regarded as probable, but confirmation is necessary. 



g, (31*13'44'0). This prism, so far as our measurements go, 

 is better established than the form i, and so is given, but it 

 has complex indices and altogether is a doubtful form. 



Crystal. Signal. Readings. 



2 



extremely poor 



13° 11' 



8 



extremely poor 



13° 22' 



14 



good 



13° 19' 



Average 



poor 



13° 17''3 



Calculated 





13° 17' 



