42 H. S. Washington — New Leucite Rock. 



These constituents and percentages show that the min- 

 eral is unquestionably a garnet, even though the molecu- 

 lar ratios do not conform strictly to those of the garnet 

 formula. This is to be attributed in part to the serious 

 errors that are almost unavoidable in the analysis of 

 such a small amount of material as was at my disposal, 

 and in part probably to the presence of some FeO, which 

 would reduce the apparent amount of R 2 0.3 an d, with the 

 MnO known to be present, would increase that of RO. 

 The ratios would thus approximate more closely to those 

 of garnet, 3:1 : 3. 



This garnet is certainly quite high in titanium, which 

 is for the most part, if not presumably entirely, present 

 as Ti0 2 . In its high titanium it resembles the melanite 

 of Beaver Creek, 6 Frascati 7 and the Perlerkopf , 8 and the 

 schorlomite of Magnet Cove, 9 but differs from the melan- 

 ite of East Rock, near New Haven, Conn., 10 which con- 

 tains none. It may be called a melanite, the name usually 

 given to the andradites (lime-iron garnets) found in 

 alkalic effusive rocks. 



Optically, it is perfectly isotropic, showing no anoma- 

 lous double refraction. The refractive index, 1-94 (Mer- 

 win), is higher than that of any garnet yet recorded, so 

 far as search of the literature reveals. Those that come 

 nearest to it in this respect are the melanite from Sys- 

 sersk (w(Na) =1-8893) determined by Osann, and that 

 from Frascati (n(Na) — 1-8566) determined by Will- 

 ting. 11 



As it was thought that the determination of the refrac- 

 tive indexes would be of interest in connection with the 

 presence of titanium in these minerals, Dr. Merwin made 

 several determinations on specimens that were kindly 

 put at our disposal. 12 The results were as follows: 



n Ti0 2 



Melanite, Rocca Monfina 1-94 8-7 



Melanite, Beaver Creek, Colorado 1-95 5.08 



Schorlomite, Magnet Cove, Arkansas 1-94 16-90 



Ivaarite, Kuusamo, Finland 201 18-98 



Melanite, East Rock, New Haven 1-86-1-88 none 



6 Larsen, Journal Wash., Acad. Sci., 4, 478, 1914. 



7 Knop, Zs. Kr., 1, 62, 1877. 8 Uhlig, Zs. Kr., 53, 204, 1914. 



9 Koenig, Proc. Acad. Sci., Phila., 1886, 355. 



10 E. S. Dana, this Journal, (3), 14, 215, 1877. 



11 Rosenbusch-Wulfing, Mikr. Physiog., I, part 2, p. 18, 1905. 



12 The specimens from Beaver Creek (collected by E. S. Larsen), Magnet 

 Cove, and Kuusamo, were given by Dr. Foshag of the U. S. National 

 Museum, from its specimens; and that from East Rock, out of the Brush 

 Collection, by Prof. Ford. 



