EMERY MINE OF CHESTER, MASS. 47 



and dark-blue bordering on black, not unlike certain varieties 

 of magnetic iron-ore; with, it there are frequently found pieces 

 of corundum of some size. The interior of the mass is free 

 from micaceous specks, such as are found in the emery of 

 Naxos. Its powder examined under the microscope shows the 

 distinct existence of more than one mineral, which are often so 

 inseparably connected that the smallest fragments contain them 

 together. The two predominating are corundum and magnetic 

 oxide of iron. 



Several specimens were submitted to chemical examination 

 from those most largely impregnated with magnetic oxide of 

 iron to those that appeared to contain the least. They all 

 consisted essentially of alumina and oxide of iron ; but I in- 

 variably found a little titanic acid and silica, and most com- 

 monly a minute quantity of magnesia. No. 1 was an inferior 

 specimen ; No. 2, the better quality of rock; No. 3, the emery 

 rock crushed and prepared for market in the form of emery ; 

 No. 4, the same, and called emery crystals. 



12 3 4 



Alumina 44.01 50.02 51.92 74.22 



Magnetic oxide of iron 50.21 44.11 42.25 19.31 



Silica 3.13 3.25 5.46 5.48 



I examined a specimen of No. 2 : grain fine, and treated 

 repeatedly with hydrochloric acid and water over a water- 

 bath; a great deal of oxide of iron and a little alumina were 

 dissolved; the residue on analysis proved to be nearly pure 

 corundum, giving 



Alumina 84.02 



Magnetic oxide of iron 9.63 



Silica* 4.81 



All the chemical and physical examinations made go to show 

 that the emery of Chester is, like all other emeries, a mixture 

 of corundum and oxide of iron — a fact that will be reverted to 

 again a little further on. 



Prof. Jackson analyzed two specimens, after digesting them 

 with nitro-muriatic acid, and has given as the composition 



1 2 



Alumina 60.40 39.05 



Protoxide of iron 39.60 40.95 



* No attempt was made to estimate the water. 



