WHITLOCK. — CRYSTAL FORMS OF CALCITE. 331 



Zone 13 = Zi 3 . — Scalenohedrons of the Zone [0772 : 7071] = 



[334 : 522]. Symbol \. 



Developing the recorded forms of this zone into a series we have : 



VI d\_ 8 _ Pi % q_._ 



29-10-26 514 816 302 412 522 



2a 5 8 oo 4 



10 ^ ^2 



ill 4 



(«) ■••4 



Referred to N4 the zone fragment between (334) and (302) is very 

 incomplete and contains the extra forms xo» To an d 8, of which the 

 latter has already been discussed under zone 2. The portion of the 

 zone between (302) and 522) contains no forms which have not been 

 already discussed. 



Q: (7-28-3o-9) = (17-10-18). This scalenohedron was noted by 

 Hessenberg 104 on crystals from Rodefiord, Iceland. Irby includes this 

 form in his list without comment; it is somewhat worthy of note, 

 however, that the hypothetical form (6-25-31-8) = (15-9-16) differs 

 from (7-28-35-9) by less than 20' of <p value and by only 1' of p value. 

 This hypothetical scalenohedron would reduce to § in the above series. 

 The form (7-28-35-9) is somewhat doubtful. 



V": (19 -36 -55-13) = (29-10-26). This scalenohedron was ob- 

 served by Gonnard 105 on crystals from Couzon, Rhone, France. As 

 in the previous instance it would seem that a hypothetical scaleno- 

 hedron could be substituted for this form. The hypothetical form 

 (6-11-17-4) = (938) gives the following values of <p and p compared 

 with (19-36-55-13): 



The above hypothetical scalenohedron would reduce to 2 in the 

 series under discussion. It is possible that the scalenohedron (19-36- 

 55-13) should be referred to the simpler indices. 



104 Hessenberg, F., Min. Notiz., 8 (1872). 



105 Gonnard, F., Bull. soc. fr. min., 20, 18 (1897). 



