TITUACOXAI. SYSTKM 



77 



: rmin.-ito asymmctriciilly in the face, on a line connecting 

 the middle points of the four equal edges. 



a : a : me 

 I. Sphenoid of the second order ; - -; 'irK(hol), iTK(ohl). 



When the poles of Fig. 141 are moved into the diametral planes, 

 the + right and l'ft sphenoids will fall in one form, the + 

 -phenoid of the second order, Fig. 142, in which the lateral axes 



Fio. 141. Type 22: Tetragonal 

 alternating. 



FIG. 142. The Te- 

 tragonal Sphenoid of 

 the Second Order. 



FIG. 142 a. The Plus 

 Right Tetragonal 

 Sphenoid of the Third 

 Order. 



terminate in the central point of the line joining the middle of the 

 four equal edges. Sphenoids of the second order may be considered 

 as derived from the tetragonal pyramid of the second order by 

 extending alternating faces above and below. 



II. Other forms. No new forms are produced by the other 

 possible positions of the poles. Forms possible to combine in the 

 type are : 



right and left sphenoids of the third order, TTK(hkl), 

 TTK(khl), irK(hkl), inc(khl). 



sphenoid of the second order, K(ohl), K(hol). 



sphenoid of the first order, K (hhl), K (hhl). 



prism of the third order, IT (hko), IT (kho) . 



Prism of the second order, (oho). 



Prism of the first order, (hho). 



Basal pinacoid, (001). 



Example. There is yet no representative of this type, either 

 among minerals or artificial compounds. 



