SCHAIXER.] 



Spodumene from Sun Diego County. 



267 



The hornblende is common green hornblende, with usually 

 ragged outline, and possesses normal optical pi*operties. 

 b = b, cAC = 16°. The pleochroism is a = light yellow to 

 light olive green, b dark olive green, C sea green to blue 

 green. The absorbtion is C > b > a. 



The triclinic feldspar predominates as is shown by the albite 

 twinning lamellae present. Symmetrical extinction angles gave 

 values from 30° to 35°, making this feldspar labradorite. 



The orthoclase occurs sparingly in nearly square sections and 

 is distinguished from the labradorite by its lower relief and 

 birefringence. 



From its structure and mineral contents the rock is evidently 

 a basiediorite containing some orthoclase. 



From a description of the other locality, the mode of occur- 

 rence of the spodumene there, seems to lie similar to that at 

 Pala, being a dike in "blue granite" (the name locally given to 

 the diorite) . 



DESCRIPTION OF CRYSTALS 



Forma, — Only the prismatic, zone is well denned on the 

 specimens seen by the writer; both ends of the crystals are 

 rounded off, and any forms oecuring there are practically unde- 

 terminable. On one of the smaller crystals, the two forms 

 s = 1 121 1 and p = J 112 J may possibly be present.* The 



Dana Gdt. 



pq = -(f + l)-i 



— 2(p+l).2q = pq 



measurement of these two forms, with the two circle goniometer, 

 gave the following results: 



Measured. Calculated. 



P <t> P 



S = 12 = \ 121 \ 37° 14' 73° 33' 38° 46' 72° 56' 

 p=— J = |T12| 21 05 31 57 20 05 34 04 



The forms in the prism zone, however, can easily be 

 determined. They are 



I, = oao = 1 010 J n = «o3 = fl30j 



a=oo0=jl00^ A= oof =r J 350 ^ 



m— oo = |110| J = fco — J 320} 



• The orientation of the crystals in this paper corresponds to the one given in 

 Goldschmidt's Winkeltabellen. To change the indices to those given in Dana's 

 System, the following transformation symbols (Gdt. Index 3) are used. 



