270 



WASHINGTON: ITAUTE 



TABLE 13 — (Continued) 

 Methylene Blue 



PETROGRAPHY.— 7to/^7^; a new leucite rock. Henry S. 

 Washington. Geophysical Laboratory, Carnegie Institu- 

 tion of Washington.^ 



Last October, while in Rome, there was brought to my atten- 

 tion by Dr. G. A. Blanc, of the University of Rome, and Ing. F. 

 Jourdain, a small piece of a very remarkable leucite rock, that 

 they had collected from a flow on the west slope of the volcano of 

 Rocca Monfina, north of Naples. I am indebted to their 

 kindness for the small specimen and for permission to publish 

 the results of my study. A full description will be published 

 later in the American Journal of Science. 



The rock is rather coarsely granular and very friable, com- 

 posed almost wholly (90 per cent) of spheroidal crystals of leucite 

 from 3 to 5 mm. in diameter. These show the twinned structure 

 remarkably well and carry few inclusions, these not being regu- 

 larly arranged. These crystals are cemented by a small amount 

 of a colorless glass, which contains many margaritic microlites. 

 There are also present, in very small amount, prismoids of 

 aegirite-augite and grains of titaniferous melanite, with rare 

 small crystals of biotite, magnetite, and apatite. The glass and 

 the microstructure show that the rock is a lava, not a tuff. 



Chemical analysis yielded the results shown in table i . 



The rock is seen to have a quite exceptional composition, and 

 shows the highest percentage for K2O yet recorded, the next 

 highest (11.91) being that of an orendite from the Leucite Hills, 



1 Received March 30, 1920. 



