Kraus and Goldsberry — Composition of JBornite. 539 



Art. XLY. — The Chemical Composition of Bomite and 

 its Relation to Other >Sulpho-Mi?ierals* ; by E. H. Keatjs 

 and J. P. Goldsbekry, with one text-figure. 



Introduction. 



In September, 1912, the Mineralogical Laboratory of the 

 University of Michigan purchased from the Ward's Natural 

 Science Establishment of Rochester, N. T., four specimens 

 consisting of well-developed crystals or crystal aggregates of 

 bornite from Bristol, Connecticut. The material was a part of 

 an old collection which had recently come into the possession 

 of this firm. As crystallized bornite is very rare, it was 

 thought advisable to study this material first crystallographic- 

 ally, and then chemically, even though some of the crystals 

 would have to be sacrificed, in order to determine whether or 

 not some light might be thrown upon the question of the com- 

 position of this mineral. 



Crystallography. 



Crystals of bornite from Bristol, Connecticut, have already 

 been studied, and according to Danaf the following forms and 

 combinations noted: (100), (110); (111), (110), (100); and 

 (111), (110), (211). On the four specimens at our disposal all 

 of these forms, with the exception of the octahedron (111) 

 were observed, and in addition the following were also noted : 

 (221), (322), (133), (411), (522), (533), and (833). Of these 

 (221), (433), (411), (522), and (833) are not listed by Gold- 

 schmidtj and, hence, are to be considered as new forms for 

 bornite. As will be shown later all of these forms, with the 

 possible exception of (411), are to be considered as well estab- 

 lished. 



Specimen 1. — This is a portion of an extremely well-developed 

 crystal, but only the faces of one octant are present. The 

 greatest length of the specimen measured about 2'5 cm . The 

 observed forms are ^(110), t (221), and *(211). Although the 

 faces are not all of a uniform size <#(110) predominates. One 

 face of i (211) is the largest on the crystal, the other two being 

 of intermediate sizes. Two of the faces of t (221) appear as 

 small triangles, the third as a narrow plane between i and d. 

 Fig. 1 shows the sizes and distribution of the various faces. 

 All planes are striated, and the orientation of these striations, 



*Kead before the Geological Society of America at the Princeton meeting, 

 January 1, 1914. 



f System of Mineralogy, 5th edition, 45, 1868. 

 % Atlas der Krystallformen, 1913, I (text), 248. 



