H. 8. Washington — New Leucite Rock. 33 



Art. IV. — Halite, a new Leucite Rock; by Hexry S. 



"Washington. 



Introduction. — Zirkel was the first, in 1867, to discover 

 with the newly introduced microscope that many basalts 

 contained microscopic leucite s, 1 and he gave the name 

 "leucitite" to such basaltic rocks which contained no 

 feldspar. The term was generally adopted, and is now 

 the recognized name for feldspar-free effusive rocks, that 

 are composed essentially of leucite and augite in about 

 equal parts. Thirty years after Zirkel 's observation, 

 Dr. Whitman Cross 2 suggested that "the term leucitite 

 be reserved for the rock that has not yet been discov- 

 ered, * * * * consisting essentially of leucite, with all 

 other minerals of subordinate importance." A similar 

 suggestion was also made for " nephelinite. ' ' 



Leucite rocks are not very commonly met with, and, 

 up to the present, no occasion has arisen to put Cross' 

 suggestion to a practical application. It is, however, 

 the purpose of this paper to put on record, and to de- 

 scribe briefly, such a true "leucitite," in Cross' sense 

 of the term, that is, an effusive rock composed almost 

 wholly of leucite. The name "leucitite," through long 

 usage, has come to connote the presence of augite, along 

 with the leucite, in almost equal amount, and with small 

 quantities of magnetite, apatite, and possibly nephelite, 

 so that rocks called leucitite are highly femic, and fall 

 mostly in salfemane. The name is one of our many 

 heritages from the early days of petrography, when the 

 occurrence of rare or unusual minerals was considered a 

 leading factor in rock nomenclature, and long before the 

 importance of the recognition of the quantitative rela- 

 tions of the mineral constituents of a rock had begun to 

 receive recognition. Under the circumstances, it is inad- 

 visable to follow Cross' suggestion, and to redefine the 

 old term "leucitite." It is better, in that it is less likely 

 to lead to confusion, to bestow a new name, and the one 

 here proposed is Halite, in honor of the country whose 

 lavas are so famous for their abundance in leucite, and 

 where, appropriately enough, the new and long sought- 



1 F. Zirkel, Zs. D. Geol. Ges., 1868, p. 97. Cf . Zirkel, Basaltgesteine, Bonn, 

 1870, p. 44. 



2 Cross. This Journal (3), 4, 137, 1897. 



Am. Jour. Sci.— Fourth Series, Vol. L, No. 295.— July, 1920. 

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