56 Washington and Wright — Feldspar from Linosa. 



An analysis was made in duplicate (except for FeO, the 

 alkalies and H 2 0) on one lot of selected fragments, portions of 

 which also served for the specific gravity determinations, the 

 material being dried at $.10°. As the results were decidedly 

 unexpected, especially in view of the preliminary optic work, 

 a second lot of fragments was analyzed, special care being 

 taken to select, so far as possible, only those showing cleavage 

 surfaces, so as to exclude any possible nephelite. The results 

 of the three analyses, with the average and the molecular 

 ratios of this last, are given below. 



I II III Average 



Si0 2 52-73 52-75 52'83 52-77 '874 



Ti0 2 * trace trace trace trace 



A1 2 3 29-34 29-54 29'63 29'50 '290 



Fe 2 3 0-67 0-75 0-53 0-65 -004 



FeO 0-17 (0-17) (0-17) 0-17 -002 



MgO 0-03 0-05 0-07 0-05 '001 



CaO 10-73 10-59 10-67 10'66 '190 



Na 2 5-40 (5-40) (5-40) 5-40 -087 



K 2 0-74 (0-74) (074) 0'74 -008 



H 2 0-38 (0-38) 0-34 0'36 



100-19 100-37 100-38 100*30 



The very small amounts of iron oxides and magnesia are 

 evidently derived from the small, opaque inclusions. Ferric 

 oxide is in excess of ferrous, bnt in the determination of such 

 small amounts the fact is not of much significance, so that the 

 figures bear out the microscopic examination in the conclusion 

 that the inclusions are of a (non-titaniferous) magnetite. They 

 also probably contain the magnesia. We may, therefore, safely 

 reject the small amounts of ferric and ferrous oxides, magnesia 

 and water, which last is to be ascribed to adsorption of 

 atmospheric moisturef by the powder. On this basis the 

 composition deduced from the analysis will be as follows : 





Linosa mineral 



(iNa 2 |Ca)Al 2 Si 3 O 10 



AbxAnj 



Ab 3 An s 



SiO n 



53-26 -882 9'09 





52-84 



55-67 



58-24 



A1 G, 



29-78 -291 3-00 





29-94 



28-26 



26-53 



CaO 



10-76 -192 1-98 





10-96 



10-34 



8-32 



Na„0 



5-45 -088) 

 0-75 -008j Uyy 





6-26 



5-73 



691 



K 2 





o-oo 



o-oo 



o-oo 



oo-oo 



10000 



100-00 



100-00 



* The color produced by H 2 2 in the solution used for the titration of iron 

 as Fe 2 3 was barely perceptible, so that only faint traces of titanium can be 

 present. 



fCf. Day and Allen, Carnegie Publication, No. 31, 1905, p. 57. 



