NEW YORK STATE MUSEUM 



the scalenohedral [fig. 25] types. In this series the combination 

 shown in figure 24 forms an additional link in the sequence of 

 development from the pyramidal to the scalenohedral types. 



Regarding the genetic relationships of the members of this in- 

 teresting series, the writer can do little more than speculate. It 

 is, however, quite apparent, from its position, which is always that 

 of close proximity to the walls of the seam, that the pyramidal type 

 occupies the lowest place in the crystal development, representing 

 the oldest generation of calcite. It is equally certain that the 

 scalenohedral type is predominant in crystals of the second gen- 

 eration which might possibly have been, in a measure, derived 

 from the re-solution of the first generation of calcite. Between 

 these limits we find a variety of expressions of crystal habit which, 

 when considered with reference to the main facts above noted, 

 leads us to seek for the solution of the crystallogenetic problem 

 along several lines. It is the opinion of the writer that, in the 

 case of the Union Springs locality at least, development in crystal 

 habit is not dependent solely on chemical or physical differences 

 in the crystallizing solutions, but is further complicated by the 

 presence of external forces. 



Occurring forms and combinations 



As previously noted, the second order pyramid y (8.8.16.3) is of 

 characteristic occurrence in the Union Springs calcites, specially 

 in those of the first generation. It is present as a series of bril- 

 liant faces giving good reflections and only in the case of the pris- 

 matic crystals shown in figure 22 does it show any tendency toward 

 merging into vicinal planes. In the above exception there appear 

 traces of a steeper pyramid which could not, however, be identified 

 from the material at hand. Figure 22 shows a prismatic habit 

 which is clearly a phase of the second generation. The crystals 

 of this habit are considerably larger than those generally noted 

 from this locality, individuals 30 millimeters in length being not 

 uncommon. Inclusions of marcasite in microscopic crystals are 

 so plentiful as to render the calcite, which would otherwise be 

 transparent, quite translucent. These inclusions are distributed 

 along planes parallel to the rhombohedron r (1101). The planes 

 of a (1120) and y (8.8.16.3) are both sharp and brilliant as are 

 also, to a lesser degree, those of n (3. 16. 19.2). As has already been 

 shown 1 the rare scalenohedron u (3. 16. 19. 2) also occurs on crystals 

 of prismatic habit at Rondout. The planes of e (01 12) are dull and 



'See page 8. 



