558 HENRY S. WASHINGTON 



forms are present. Plagioclase is almost wholly lacking. Its 

 specific gravity is 2.31 1 at 26° C. 



With the leucitites may be classed the rock from a flow at 

 the Osteria di Biagio, on the road from Orvieto to Bolsena. It 

 is rather a nepheline leucitite, as it contains considerable nephe- 

 line in the groundmass. Its rather dark greenish gray ground- 

 mass is compact, but shows some narrow vesicular cavities, 

 generally in planes parallel to each other as determined by the 

 flow. In the groundmass are many small clear leucite pheno- 

 crysts and a few small black augites. Into the cavities project 

 very many small stout hexagonal prisms of nepheline, which are 

 coated with an opaque white substance, but are clear grayish 

 white within. 



Its appearance in thin section closely resembles that of the 

 leucitites already described, the leucites being round, with feeble 

 double refraction, and with included rings of augite microlites. 

 The pyroxene of the interstitial groundmass is an sgirine-augite, 

 and the base generally exhibits faint double refraction. Exam- 

 ination with acids shows that this is largely nepheline, though 

 a small amount of glass seems to be present. No crystal sections 

 of nepheline were to be found, and in the body of the rock it 

 acts as cement and is undoubtedly the last product of crystalli- 

 zation. In the groundmass a few small colorless laths were to 

 be seen which may be referred to orthoclase, indicating a transi- 

 tion toward the leucite-phonolites. 



As phenocrysts appear large and much cracked leucites, green 

 augites, a few fair-sized crystals of orthoclase much broken and 

 corroded, which are usually associated with the augite and appear 

 to belong to the same period of crystallization, and finally a 

 a few remains of biotite crystals altered as usual to a granular 

 mass of augite arid magnetite. The interior of one of these last 

 contains fine parallel straight lines of minute magnetite grains 

 lying at an angle of about 60° with the basal plane. 



The leucitites described by Klein agree on the whole so closely 

 with the above that it is needless to do more than refer to them. 

 Analysis No. 8, page 565, of the leucitite of Sassi Lanciati, has 



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