WOLFF: LEUCITE-TINGUAITE FROM BEEMERVILLE, N.J. 275 



areas in which three elements occur. The most abundant is orthoclase, 

 identified by its index of refraction lower than balsam, cleavages, and 

 biaxial character; the analysis shows it can contain little sodium. 

 Nepheline comes next, identified by its higher index, and lastly there 

 are some isotropic areas of very low index with irregular cracking which 

 are probably analcite. 



A little biotite, calcite, fluorite, quartz, brilliantly polarizing can- 

 crinite(l) and small areas of indeterminate zeolites are in insignificant 

 amount. Grains of pyrite are scattered through the rock. 



Analysis. 



The analysis was made essentially according to the methods used by 



Hillebrand. 1 While it shows the general chemical characters of allied 



tinguaites, yet a striking difference is shown in the predominance of 



ferrous over ferric iron, combined with the high and nearly equal amount 



of the alkalies. The ferrous iron determination was made in duplicate 



by the hydrofluoric acid method, using a doubly tubulated bell-jar and 



sand bath instead of the water bath of Cooke (Pebal-Doelter method, 



see Jannasch, " Leitfaden der Gewichts- Analyse," p. 269), and the two 



determinations differed by only 0.02 per cent. The only mineral in the 



rock containing iron (except pyrite, which is separated in the tabulation, 



and a little biotite, etc.) is the pyroxene, and this is almost all in the 



ground mass where it has the optical characters of aegirine or aegirine- 



augite. A glance at the molecular proportions will show that there is an 



excess of the alkalies over the (AlFe) 2 3 of 21 molecules and as there is 



no sodalite present it seems necessary to suppose this excess in sodium 



present in the pyroxene, where it must be combined in some way with 



ferrous and not with ferric iron, as would be the case were it aegirine. 



To better illustrate the difficulty, if we use all the ferric iron, with one 



sixth ferrous, and the proper soda for aegirine proper, distribute part 



of the remaining soda and the potash with the proper alumina and 



silica between nepheline and orthoclase, part of the ferrous iron with 



the lime and magnesia in the hedenbergite molecule, we will find with 



3 per cent in the rock of aegirine, 13 per cent hedenbergite and 6 per 



ii 

 cent of a compound Na 2 Fe(Si0 3 ) 2 . The investigations of Merian a 



and Mann 8 indicated that aegirine-augite contained sodium in some 



1 Bull. U. S. G. S., No. 176. » N. J. Min. B. B., III. 1884, p. 252. 



8 N. J. Min. B. B., II. 1884, p. 172. 



