i9o6] TRAVIS— PYRITE FROM CORNWALL. 141 



Crystal 15 shows two octahedron faces, (iii) and (iii), and a 

 portion of (102). One face of the trisoctahedron is present, in the 

 position (212). It is a trifle less than i mm. wide. (537) Hes 

 in the zone of (m) and (102) ; it is about 0.5 mm. by 0.2 mm. in 

 extent. (425) appears as a nearly equilateral triangle about 0.2 

 mm. on a side between (212), (537) and (iTi). A portion of 

 (210) is present below (212). (425) lies in the zone (210, 212). 

 Fig. 4 shows this combination of forms. 



Zonal Relations of Type I. 



The zone of trisoctahedrons, symbol (iio), seems to be the most 

 important in this type. It affords the greatest number of forms, and 

 determines the growth figures on the pyritohedron face and the 

 direction of one set of striations on the octahedrons. 



The zone of (m) and (210), symbol (121), which is usually 

 well developed in pyrite, seems to be of secondary importance in 

 this type. While it determines the second set of octahedral stria- 

 tions, it was only observed on three crystals, — 2, 11, and 15. On the 

 last two of these, however, it affords a good series of forms, (531), 

 (321), (753). (432), and (14.11.8). 



The zone (112) is important, affording (421), (13.7.3), (95^) 

 and (531), but curiously enough only a single face of this zone 

 appears at a time. The primary importance of the zone of trisocta- 

 hedrons again appears in the fact that each of the above faces lies 

 between (210) and a trisoctahedron of simple ratio, thus, — 



210 



and 531 



III 



These trisoctahedrons have the same ratio as the ones above, but are 

 in a different zone. 



The occurrence of the zone of trisoctahedrons as an important 

 zone is so rare in pyrite that the writer has been moved to call this 



