166 



GLENDONITE FROM THE LOWER MARINE SERIKS, 



The measurement of the angles between s and /, and s and m was 

 too unsatisfactory, on account of rough and curved surfaces. Fig. 3 

 is an ideal stereographic projection of one end of a crystal with 

 the three forms developed. 



Fig. 3. — Stereographic projection of one end of a 

 glendonite-crystal. 



A number of the crystals show a series of parallel striations, 

 representing the trace of a cleavage ( Figs. 5-6). In some cases, 

 these striations persist along the whole length of the crystal, over 

 forms which are not in one zone, and so cannot represent oscilla- 

 tory combinations. The angle between the plane of these striations 

 and the edge (110) (llO), was easily calculated, and proved to be 

 approximately 66°. If the original mineral were glauberite, the 

 cleavage is perfect, parallel to (001), so that the angle just mea- 

 sured, would represent /?. In glauberite, f3 is 67° 49' 7", so that 

 the angle obtained for these glendonites, is quite as close as could 

 be expected from contact goniometer-measurements. 



