Read and Knight — Re-formation of Soda-Leuoite. 295 



jected to the highest heat of a Bunsen burner for 5-| hours. 

 No noteworthy changes could be observed in a thin section 

 made from the crystal thus treated. 



Another specimen was then subjected to a constant tem- 

 perature of 1225° C. in an electric furnace for ten hours. 

 After cooling, a microscopic examination of the crystal in 

 thin section showed parts to be isotropic. There still remained 

 a considerable proportion of unalted orthoclase and nephelite. 

 JSTo traces of biotite or scapolite could be detected. The 

 chlorine at this temperature would have been driven off, and 

 with it perhaps some of the other constituents. The outer 

 border was much darker in color and presented a glassy 

 appearance. It was evident that the biotite had migrated to 

 the border, forming a fused coating which had cemented the 

 lower side of the crystal to the crucible. The shape of the 

 crystal had not appreciably changed. The thin section showed 

 the crystal to be full of globular holes about 'l mm in diameter, 

 due perhaps to the loss of volatile constituents and the passage 

 of the biotite to the outer border. 



Even granting that the isometric material which had formed 

 was leucite, the difficulty of distinguishing it from glass is 

 obvious. It was considered that the temperature employed 

 was too high, since the edges of the crystal had a glassy and 

 fused appearance, while the object of the experiment was to 

 effect, if possible, the change of pseudo-leucite into soda-leucite 

 in the solid. 



Another crystal was therefore subjected to a constant tem- 

 perature of 1100° for 8 hours. In this time a small area had 

 become isotropic and showed a few bubbles, but otherwise 

 was clear and colorless. The biotite had fused to a dark glass 

 but had apparently not migrated from its original position. 

 No scapolite could be detected ( the chlorine had of course 

 been driven off at this temperature ), but otherwise than in 

 these respects the appearance of the section had not been 

 markedly changed beyond a distinct accentuation of the relief. 



At this point it became necessary to discontinue the work 

 for the present. If opportunity shall permit, it is the hope 

 to continue it to more definite conclusions, but in the mean- 

 while it seemed wise to give an account of the preliminary 

 work, as suggestive for discussion and perhaps research by 

 others. 



Both the authors are greatly indebted to Dr. M. N. Bolles 

 of the Department of Metallurgy, who kindly conducted the 

 heating in the electric furnace. 



Department of Geology, Columbia University. 



