198 



PHYSIOGRAPHY. 



Feldspar. 



Fig. 189. 



In order to render more easily intelligible the changes 

 suffered by the primary form, ihe planes M and T have the 

 same position given them in the secondary forms, as in the 

 figure by which the primary is illustrated. Fig. 183. (uni- 

 taire. HAUY.) M on y = 90. H. P on */ = 99 29'. H. 

 Fig. 184. (prismatique. HAUY.) M on 7 = 120. H. 

 Pon/=lll 40'. H. Fig. 185. (binaire. H.) Ton/ 

 = 60. Fig. 186. (ditetraedre. H.) P on #=128 51'. H. 

 Fig. 187. (sexdecimal H.) x on y = 150 45' 28". H. 

 M on s=H6 20'. H. Fig. 188. (synoptique. H.) 

 T or M on z = 1 50. M or P on n = 1 35. q on x = 

 164 40'. H. q on a = 149 10 7 . P. This is a reunion of 

 all the modifications of Feldspar. Crystals agreeing with 

 it, with the deficiency of planes n q and y, are found at 

 Greenfield, near Saratoga, (N.Y.) ; also at Haddam, (Conn.) 

 Others, only wanting planes n and </, occur at Governeur, 

 St. Lawrence co. (N.Y.) Fig. 189. This is an elonga- 

 tion of Fig. 187, in the direction of the edge between P ajid 

 M. Fig. 188, suffers the same elongation in the direction 

 of the plane n. 



