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,, 

 "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 iia— iib consisting 

 •of no less than ii 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 I (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 / (0445), A 

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

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

 defined, y (8.8.16.3) the predominating pyramid of types III and 

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

 by oc (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 Cj (3472) are present as 

 large and well developed forms. The positive scalenohedrons u 

 (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 iib which was probably due to- 

 some twinning tendency,^ 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 



iln this connection, it is interesting to note that the calculated values of (ft for (21^1) and (42 6 1^ 

 differ by but 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. 



