Penfield and Ford — Stihiotantalite. 



65 



the vertical than the horizontal direction. The largest crystal 

 of the types illustrated is shown in about natural size in figure 

 13, which measured in the direction of the a, o and c axes, 

 respectively, 6x25x30 mm , while the remaining ones average 



10 



11 



12 



about one-fourth this size. Figure 14 shows in detail one of 

 the corners of the crystal idealized in figure 13 ; it is rather 

 unusual in showing the t] and 77', and w and w faces with 



13 



14 



numerous reentrant and salient angles, while the g and g' faces 

 are finely striated and round into one-another. At the opposite 

 end of the crystal the rj and w faces appear without reentrant 

 angles. 



An. Jour. Sci.— Fourth Series, Vol. XXII, No. 127.— July, 1906. 

 5 



