66 Buddington — Natural and Synthetic Melilites. 



various dealers in the United States. Dr. H. S. Wash- 

 ington of this laboratory also obtained for the writer sev- 

 eral specimens of the Capo di Bove melilites from Pro- 

 fessor F. Millosevich of the University of Rome. These 

 specimens proved of exceptional interest and afforded a 

 melilite of composition different from any hitherto 

 reported from this locality. The writer is greatly 

 indebted to Professor Millosevich for his courtesy and 

 generosity in sending these specimens. 



Four samples of the minerals of this group were 

 obtained in sufficient purity for analytical purposes, and 

 Dr. H. S. Washington very generously made the chemical 

 analyses. The writer wishes to express his appreciation 

 of this service. 



Separation of material. — The samples of humboldtilite 

 studied were obtained by crushing the rock containing 

 them as an accessory constituent to a sufficient fineness to 

 pass a 35 mesh sieve. The lighter components, mainly 

 nephelite and leucite, were separated with bromoform, 

 and the pyroxene by means of an electro-magnet. After 

 this treatment the samples were examined under the 

 microscope and found to be sufficiently pure. 



The densities given for the minerals represent the 

 density at 25° of the solutions in which the heavier por- 

 tion of the purified materials sank. 



Akermanite. 



Akermanite was first named and described by Vogt 

 from its occurrence in artificial slags long before its dis- 

 covery in nature. The mineral akermanite was identified 

 by Zambonini 11 at Vesuvius and its properties are given 

 by him as follows: tetragonal, cleavages 001 and 110; 

 density 3.12; uniaxial, positive; for sodium light, 

 ^ = 1.6332, ne~~n u =0.006. The compound 2CaO.MgO. 

 2Si0 2 was obtained by Ferguson and Merwin 12 and cor- 

 related by them with the mineral akermanite as a result 

 of a study of its optical characters, which are given by 

 them as tetragonal, uniaxial positive, for sodium light 

 nco =1.631 andne =1.638. The density was determined 



11 F. Zambonini, Mineralogia Vesuviana, p. 255, 1910. 



12 Op. cit., pp. 118 and 122. 



