On Nepheline-basalt from Yingé-mên, Manchnria. 13 



specific peculiarities worthy of note, showing exceptionally high 

 percentages in CaO, and H2O. Microscopic volumetric analysis 

 made with J. Hirschwald' s planimeter-ocular showed 30 per 

 cent of nepheline and nearly 15 per cent of olivine, the latter 

 value heing only approximative, due to the phenocrystic habit 

 and irregular distribution of the crystals in the microscopic field 

 (PL I.ßgs. 2 and 3). 



The presence of large amounts (45.5%) of feldspars, as they 

 are expressed in the above norms, is to my mind a paradox, as 

 basaltic glass is scantily present in the rock in which at least the 

 feldspar molecules must be assumed to exist. Otherwise they must 

 be looked for in the composition of nepheline. 



The chemical composition of nepheline has long been a problem 

 much discussed among mineralogists. Lately Foote and Brad- 

 ley'-* have offered an explanation, namely, that a substance on 

 crystallizing may form ' ' a solid homogeneous solution with foreign 

 matter," and that the mineral nepheline consists of a pure com- 

 pound, probably NaAlSi04, with a varying amount of dissolved 

 silica. Very recently, W.T. Schaller^^ has proposed still another 

 explanation, viz., that the mineral nepheline is an isomorphous 

 mixture of the compounds crystallizing in the hexagonal modifica- 

 tion, which are AlNaSiOj (essential component), AlKSiO* (kalio- 

 philite), and AlNaSisOg, the last being only in mixture in 

 nepheline, and being best known in its triclinic form as albite. 

 He says "the remarkable fact that the compound KAlSi04 is 

 always present to the extent of about 20 per cent has as yet 

 received no adequate explanation." The albite molecule in 

 nepheline, however, varies from 5.6 to 10.6 per cent. At all 



1) "On solid solution in minerals with special reference to nephelite." Amer. Jour. Sc/i., 

 4tli ser., 31 : 25. 1911. 



2) " The chemical composition of nephelite." Jour. Washinftton Acad. Sei., Vol. 1. No. 4. 

 September, 1911, pp. 109-112. 



