Kozu and Washington — Augite from Stromboli. 407 



43° 20' with the edge (010) A ( 100) in the acute angle made 

 by (100) and (101). 



From this description it will be seen that the Stromboli 

 augite is somewhat different from common augite, in the 

 lower refractive indices, in the higher birefringences 

 (7 — a) and (/3— a), and in the smaller angles of the optic 

 axes and of the extinction. These characters seem to 

 suggest that the Stromboli augite contains somewhat 

 larger quantities of the diopside molecule than com- 

 mon augite. 



Chemical Characters. 



The material used for chemical analysis was very care- 

 fully selected. A lot of good-sized crystals was coarsely 

 crushed and fragments from the interior, not contam- 

 inated by adherent scoria, were picked out by hand under 

 a lens. These were almost quite free from inclusions, 

 very few and small grains of magnetite being seen in 

 some of them. The amount of these was not sufficient 

 to affect the study of the chemical composition. The 

 specific gravity of the selected fragments was 3-243 at 

 19°. The analysis was carried out by the usual methods. 

 Three precipitations with ammonia were made, to ensure 

 a complete separation of MgO from A1 2 3 . Ti0 2 and 

 MnO were determined colorimetrically. The alkalies 

 were determined by the Lawrence Smith method. The 

 results are shown in Column A of Table 1. 





1 



Table I. 



Analyses 



OF AUGITES. 









A 



B 



C 



D 



E 



Aa 



SiO. 



50-94 



5013 



50-88 



51-27 



49-42 



•849 



TiO, 



0-96 



1-91 



102 



0-70 



0-55 



•012 



Al 2 6 3 



3-37 



7-08 



5-36 



305 



428 



•033 



Fe 2 3 



205 



l-icr 



1-21 



3-08 



2-86 



•013 



FeO 



7-41 



441 



467 



434 



5-56 



•103 



MnO 



010 



005 



trace 



0-28 



010 



•001 



NiO 



n. d. 



002 



u.d. 



003 



n. d. 





MgO 



1459 



13-73 



13-78 



14-21 



13-58 



•365 



CaO 



20-34 



2006 



22-96 



22-58 



22-35 



■363 



SrO 



008 



u. d. 



11. d. 



none 



n.d. 



•001 



Na,0 



0-61 



1-88 



0-50 



0-67 



1-04 



•010 



K,6 



0-18 



0-25 





006 



0-38 



•002 



H,0+ 



0-08 



011 



0-34 



n. d. 



n.d. 





H,0— 









none 



009 





100-71 100-73 100-72 100-27 100 21 



