36S Hymlrnan and Bonney — Analysis of Sp/tcralites. 



then transferred to a platinum dish and heated over the blowpipe, 

 the loss of weight being taken as equal to the combined water. The 

 iron was determined in each case by the titration of an aliquot 

 part of the solution, the result being calculated to Fe 2 O s in the 

 case of the spherulite, and to Fe in that of the matrix ; since 

 a preliminary test showed that this contained a considerable 

 quantity of Fe 0, with probably a little Fe 2 3 . 



The alkalies were determined by heating the finely-powdered rock 

 with ammonium chloride and calcium carbonate, treating with water 

 and precipitating the bases from the solution ; the potassium was 

 then separated, and weighed as potassium platino-chloride. 



In the analyses of typical felspars, taking the A1 2 3 as unity, the 

 other constituents occur in the following proportions : — 



Orthoclase. Albite. 



1 



3-50 



... 0-60 



If, then, in the above analysis of the spherulite we suppose the K 2 

 to be present in orthoclase and the Na 2 O in albite, we find, using 

 these proportions, that the alumina is almost exactly the amount 

 required, and that about 28-5 of the Si 2 remains : that is to say, 

 the spherulite must consist almost entirely of albite, orthoclase, free 

 quartz, and some ferric oxide, and there is, roughly speaking, three 

 times as much albite as orthoclase, the felspars making up rather 

 less than two-thirds of the mass. 



In the matrix the felspars occur in smaller quantity and in more 

 nearly equal proportions (the albite still dominating), and there is 

 a larger amount of free quartz. 



Both these analyses could find parallels among the published 

 bulk-analyses of felsites or volcanic glasses. Both (before devitri- 

 fication) would represent dacit.es. but the matrix has the nearer 

 relation to the rhyolites. These analyses accord with the con- 

 clusions of Lagario, especially in the larger proportion of soda in 

 the spherulite, and in most of the cases given by him the silica 

 pei-centage is higher in the matrix. 



The following analyses of a spherulite and of the matrix are given 

 by Michel Levy (Bull. Soc. Geol. France, v, 3rd series, p. 248). 

 Spherulite. Matrix. 



Oxygen ratio. Oxygen ratio. 



Loss on heating ... 2-00 5 4 27 



RO : R 2 0, : Si 2 7-56 : 898 : 30-34 10 40 : 10-35 : 24'04 



