62 NEW YORK STATE MUSEUM 



on the rhombohedral planes in parallel position; these latter, how- 

 ever, are microscopic and only serve to accentuate the character- 

 istic grouping habit. 



Type V. Crystals of this type were noted on a single specimen r . 

 which differed little, with respect to the association and general 

 deposition of the secondary minerals, from the specimens producing 

 types III and IV, but which showed a much lower percentage of 

 secondary quartz crystals than these latter. Several small crystals 

 of transparent apatite were noted on this specimen. In habit these 

 crystals are far more complex than any hitherto described from, 

 this locality, the combination shown in figures na-nb consisting 

 of no less than n forms. In size and brilliancy they also exceed 

 the previously described types averaging 12 mm in vertical length 

 and beautifully developed in clear and sharp faces, all of which, 

 with the exception of / (0445) gave fine reflections of the goni- 

 ometer signal. In general, indications seem to connect this type 

 with a slower action of the crystallizing solution producing more 

 perfect and highly modified individuals. 



A clearly marked rhombohedral zone consisting of I (0445), A 

 (0443), /(0221), A (0772) and 2 (o.ii.ii.i) characterizes the 

 crystals of this type, the faces of which are small but clearly 

 defined. 7 (8.8.16.3) the predominating pyramid of types III and 

 IV is wholly lacking from this combination, its place being taken 

 by cc (4483) a form not hitherto noted from this locality but 

 which completes the series of pyramids by supplying a logical 

 link in the sequence between (2243) and (8.8.16.3) the former of 

 which is present as a highly developed series of planes giving very 

 fair reflections. Two negative scalenohedrons p; (2461), which 

 was also noted in types II and IV, and C; (3472) are present as 

 large and well developed forms. The positive scalenohedrons v 

 (2131) and R: (8.4.12.1) are present as well developed forms. A 

 regular and symmetrical roughening was noted on the obtuse polar 

 edges of v (2 131) as shown in figure 11b which was probably due to 

 some twinning tendency, 1 although no twins were observed in con- 

 nection with this type. 



The complex zonal relations between the various forms occurring 

 on the calcite from Lyon Mountain are shown in the stereographic 

 projection, figure 12 and are particularly well illustrated in the 



1 In this connection it is interesting to note that the calculated values of (p for (2131) and (4261)- 

 differ by tmt 30" and that consequently a penetration twin parallel to (0001) would bring the 

 superposed planes of these two forms in close orientation and might result in a vicinal roughen- 

 ing similar to that observed. 



