Mr. L. Fletcher's Crystallog rapine Notet 



287 



If001.101 = 



1 



44° 34^' 



44° 22V 



44° 22' 



44° 2H' 



Calculated. 



1 



108 40 



70 7* 



1 23* 

 0" 



20 59 

 22 41 



108 17} 



69 56 



2 3 







20 12f 



22 42| 



108 16} 

 69 55*, 



2 4} 





 20 10| 

 22 42| 



108 15 J 

 69 55 



2 6 





 20 8f 

 22 42| 





1 



. J Nauru... J 

 °°i \Haid. ...; 

 t t ] Nauru....' 

 A MHaid. - 



Obserted. 



108° 17i' 

 69° 54f'-70° 0i'. 

 mean 69° 59}' 



2° 3' 

 20° 9' 



From a third crystal not quite so perfect, but still giving 

 very good images, the angle w 2 &/ 2 was determined to be 

 108° 18f . 



There can thus be no doubt that: — 



1st. The growth is strictly regular. 



2nd. The parametral angle differs from that determined from 

 other specimens by previous observers, and is very nearly 

 44° 22'. 



3rd. The twin-plane is a face of the form {101}. And 



4th. The composition-plane is parallel (and not perpendicu- 

 lar) to the twin-plane. 



At the suggestion of Prof. Maskelyne, a careful analysis of 

 this specimen was made in the departmental laboratory, with 

 the view of ascertaining to what extent this variation in the 

 fundamental angle is attended by a difference from the che- 

 mical composition of ordinary copper pyrites. The following 

 results were obtained by Dr. Walter Flight: — 



Copper 



Iron 



Sulphur 



Arsenic 



Quartz 













Calculated 



I. 



II. 



CuFeS,. 



25-78 



30-66 



34-45 



35*16 



34-11 



30-57 



37-52 



[35-23 bv diff.] 



34-98 



traces 







0-28 







98-74 



100-00 



100-00 



No other metals were discovered, although carefully searched 

 for. The specimen is thus found to contain a considerable 

 and variable excess of FeS 2 over that of typical copper 

 pyrites — the first analysis corresponding very nearly to 

 Cu FeS 2 + i Fe S 2 , and 'the second to Cu FeS 2 +\ FeS 2 . As 

 close examination of the specimen reveals the presence of 

 included minute crystals of iron pyrites (and mispickel), it is 

 possible that even in the second fragment, which was specially 



