WHITLOCK. — CRYSTAL FORMS OF CALCITE. 301 



The portion of the zone between (0112) and (0221) is extremely 

 rich in forms, no less than 28 rhombohedrons having been recorded 

 between_these limits. Prominent zone intersections occur at (Olll) 

 and (0332), which suggest these poles as knot points. Splitting at 

 these points, the forms in the first portion are : 



This portion of the zone is incomplete and contains the extra forms 

 S> n> V anc ^ 9- Of these the first and last are obviously extremely 

 close to the knots and might possibly have been due to vicinal develop- 

 ment. 



a. (0-11 -IT -20). This rhombohedron was observed by Hobbs 29 

 on calcite crystals from southern Wisconsin. Prof. Hobbs in discuss- 

 ing this form suggests that it may be due to corrosion. 



b. (0-18-18-25). This rhombohedron was also observed by Hobbs 29 

 on the afore mentioned occurrence. It is worthy of note that the 

 hypothetical rhombohedron (0- 13-13- 18), which reduces to f in 

 the above series comes 5' nearer to the measured angle as given by 

 Hobbs. The form is doubtful. 



t>. (0- 14-14- 17). This rhombohedron was noted by Schaller 30 on 

 crystals from Hillsboro, New Mexico. The form, which was estab- 

 lished from 3 measurements with the two circle gonimeter, seems more 

 rational than any other of the extra forms in the series. The hypo- 

 thetical rhombohedron (0556) which would reduce to 2 in the normal 



29 Hobbs, W. N., loc. cit. 



30 Schaller, W. T., loc. cit. 



