Measurement and Cleavage of certain Primitive Crystals. 243 



Nothing having been said in my papers on the oxide of tin, 

 and the sulphate of barytes and quartz, on the mode of cleaving 

 them, they are now placed in the following table at the head of the 

 ten substances forming the particular objects of this communication, 

 chiefly to allow the opportunity of saying a few words on the 

 subject of splitting them. 



Substance. 



Primitive Crystal. 



References to Plate 12. 



Measurements. 



According to 

 Haiiy. 



Accord- 

 ing to 

 Bournon 



By the 

 Reflecting 

 Goniometer 



Oxide of Tin 



An obtuse octohedron of T 

 which the common base of > 

 the pyramids is square. J 

 Haiiy. 



Fig. 1. P on P 



P on the opposed 

 plane over the apex 



67° 42' • 





67° 50' 

 112° 10' 







Sulphate of 

 Barytes 



A right prism, with ) 

 rhombic bases. \ 

 Haiiy 



Fig. 2. M on M 



M on the adjacent 

 plane, over the 

 edge A. 



101" 32' 13" 

 78» 27' 47' 





101° 42' 

 78° 18' 



Quartz 



A slightly obtuse rhom- ) 

 boid. Haiiy. J 



Fig. 5. P on P 

 P on P' 



94° 24' 



85° 36' 





94° 15' 

 85° 45' 



Zircone 



An obtuse octohedron ; ~l 

 the common base of the £ 

 pyramids is square. Haiiy. J 



Fig. 1. P on P 



P on the opposed 

 plane over the apex 



82° 50' 





84° 20* 

 95° 40' 



Staurotide 



A right rhomboidal prism 

 Haiiy. 



Fig. 2. M on M 



M on the adjacent 

 plane over the edge 

 A. 



129° 30' 





129° 20' 

 50° 40* 







Anatase 



An acute octohedron ; ~) 

 the common base of the £• 

 pyramids is square. Haiiy. J 



Fig. 4. P on P 



137° 10' 





136° 47' 



Specular Iron 



A slightly acute rhom- ) 

 boid. Haiiy. J 



Fig. 3. P on P 



87° 9' 

 92° 51' 





86° 10* 

 93° 50' 



Diopside 



An oblique rhomboidal ) 

 prism. Haiiy. ) 



Fig. 6. M on M 



M on the adjacent 

 plane, over the edge 

 A. 



87° 4'2' 





87° 6' 

 92° 55' 



