RE-EXAMINATION OF AMERICAN MINERALS. 137 



Considering the alumina as replacing silica, these give the 

 oxygen ratio of pyroxene and the formula fi 3 (Si, 3el) 2 . 



31. Jenkinsite. 



The green mineral that occurs in velvety coatings on the 

 magnetite of O '.Neil's Mine, in Orange County, New York, has 

 been described by Prof. Shepard,* as a new species. Its in- 

 timate association with magnetite renders it somewhat difficult 

 to obtain it perfectly pure ; but by placing the fine particles 

 of jenkinsite in a vessel of water, and stirring the mass with a 

 clean rod of soft iron that passes through an electro-magnetic 

 coil in connection with a battery, every particle of magnetic 

 iron is removed. Two' different portions thus purified, pro- 

 cured at different times from Mr. Silas E. Horton and Mr. John 

 Jenkins, gave 



1 2 



Silica 38.97 37.42 



Protoxide of iron 19.30 20.60 



Protoxide of manganese 4.36 4.05 



Magnesia 22.87 22.75 



Alumina 53 .98 



Water 13.36 13.48 



99.39 99.28 



From these we obtain the mean oxygen ratio for silica and 

 protoxides, and water, 19.84 : 14.50 : 11.92=4 : 3 : 2J, and the 

 formula ft 9 Si 4 +7H. 



Atoms. At. weight. Per cent. 



Silica 4 2309 38.83 



Magnesia 6 1500 25.23 



Protoxide of iron 3 1350 22.70 



Water 7 788 13.24 



5947 



The mineral is similar in composition to serpentine with one 

 atom more of water, and the magnesia replaced in part by 

 protoxide of iron and manganese. It also has a strong resem- 

 blance to hydrophite, both in chemical and physical properties. 



32. Lazulite. 



This species occurs in considerable abundance in Sinclair 

 County, North Carolina, at present the only American locality. 

 It is of interest to compare its composition with the European 



* Amer. Jour. Science and Arts, 2d series, xiii, 392. 



