H. S. Washington — New Leucite Rock. 39 



biotite and diopside. Similar to this as regards potash 

 (though with differ ences in silica, alumina, etc., as may 

 be seen in the table), are a leucite sanidinite from Monte 

 Somma (3), a tavolatite from the Alban Hills (4), and 

 a vicoite from Eocca Monfina (5). The analysis of a 

 typical, so-called "leucitite" is given in (6) ; for com- 

 parison. This contains only about 32 per cent of modal 

 leucite, and about 50 per cent of augite. 



The amount of soda is about that shown by most 

 Italian leucites. The preponderance of ferric over fer- 

 rous oxide and the rather high lime are to be noted and, 

 among the minor constituents, the rather high figures for 

 S0 3 and BaO. The common occurrence of noselite (and 

 hauyne) in Italian leucitic lavas has already been men- 

 tioned, and S0 3 is present in all the lavas of the Leucite 

 Hills. It has been pointed out elsewhere 4 that barium 

 shows a tendency to be associated with magmas that are 

 high in potash, as is well seen in the leucitic lavas of 

 Italy and of Wyoming. In the present rock it may be 

 assumed to be present in the leucite. As the literature 

 furnishes no analysis of leucite in which BaO has been 

 determined, this determination was made on a crystal 

 from Vesuvius ; the amount found was 0-08 per cent. It 

 is therefore reasonable to suppose that it is present in 

 the leucite of the italite, though in larger amount than in 

 the leucite of Vesuvius. 



Classification. — The data for the classification of the 

 italite specimen according to the Quantitative Classifi- 

 cation are given in the calculated norm, shown below. 



1 



92-12 



•56 



Anorthite 2-78 2-78 



Leucite 82-62 "] 



Nephelite 4-83 [_ 



Kaliophilite 0-47 f 89d4 



Thenardite 1-42 J 



Diopside 0-86 \ q QQ ~] 



Wollastonite 3-13 ] dyy L 



Magnetite 0-23 1 f 



Ilmenite 1-06 }■ 2-57 J 



Hematite 1-28 J 



Norm of Italite. Eocca Monfina. 



The rock therefore falls in Class I, Persalane (C. I. P. 

 W.) ; order 9, laurentare (Adams) ; rang 1, congressase 

 (Adams), and subrang 1: the symbol for the specimen 

 analysed is I. 9. 1. 1. 2). This perpotassic subrang has 



4 H. S. Washington, Eoman Comagmatic Eegion, Carnegie Publication 

 No. 57, p. 188, 1906; Trans. Am. Inst. Min. Eng., 1908, p. 754. 



