268 



University of California. 



[Vol. 3. 



The measurement of the angles of these forms with those 

 calculated, are given in the following table. 



Measured. Calculated. 



4> p 4> p 



h = 



Ooo = 



{oioj 



0° 



06' 



90° 00' 



0° 



00' 



90° 00' 



a — 



coO = 



{100} 



90 



00 





90 



00 





m = 



co = 



[110] 



43 



30 





43 



30 





n = 



so 3 = 



|l3Gj 



17 



00 





17 



33 





A 



co i = 



|350j 



29 



50 





29 



39 



i < 



I = 





i320| 



55 



01 





54 



54 





The form A = -eo-f = J 350 ^ is new for spodumene and occurs 

 but once, as a small face. 



The form n - - «3 = fl30| was measured by means of a 

 wax impression, as the crystal on which it occurs is too large for 

 measurement with the reflection goniometer. 



The unit prism is always present, and measurements of ten 

 faces gave the following values: 



<t> angle on m = °o = \110\ 



43° 30' 43 31 



43 29 43 28 



43 36 43 20 



43 24 43 33 



43 33 43 30 



Av. = 43° 30' 



This value agrees with the one given by Dana in his System, 

 but varies somewhat from the angle obtained by Brush and 

 Dana* on cleavage faces of the Branchville, Conn., spodumene, 

 their results giving 43° 36.5' 



The interfaeial angles on the large crystals were measured 

 with a hand goniometer and the averages of these measurements 

 are shown in the following table. 



Measured. Calculated. 

 (110) : (HO) 93° 18' 93° 00' 



(110) : (T10) 87 24 87 00 



(1UI) : (010) 44 00 43 30 



(110) : (100) 46 36 46 30 



(100) : (OKI) 89 30 90 00 



The unit prism, while always present is not always equally 

 developed in its four faces, two parallel faces being frequently 



*Amer. Journ. ^Science, 1880 (3), 20, 257. 



