EMERY MINE OF CHESTER, MASS. 51 



MINERALS ASSOCIATED WITH THE EMERY OE CHESTER. 



Corundum. — This mineral, as might naturally be expected, is 

 found with the emery, sufficiently distinct and separate to be 

 at once recognized, sometimes in thin seams, massive in its 

 character, but more commonly in flattened crystals of small 

 dimensions. 



Diaspore. — Very excellent and beautiful specimens of this 

 hydrate of alumina have been found at this emery locality; it 

 is often in distinct and separate prismatic or bladed crystals, 

 quite colorless and transparent. 



Emerylite or Margarite. — Some of the finest specimens of 

 this mineral that are known have been found at this locality. 

 It will be seen by referring to my former papers on emery that 

 I first discovered this mineral associated with emery ; its com- 

 position showed it to differ from any other then known mineral. 

 I compared it subsequently with margarite, which had been 

 discovered before, and suspected the identity of the two min- 

 erals; but as the analysis made out and accepted as the com- 

 position of margarite did not accord with that of emerylite, 

 I undertook to re-examine margarite, when I found that its 

 composition had been erroneously determined, and that it was 

 in fact the same mineral with emerylite, which last name has 

 had to yield to the priority of date of the other. 



I have analyzed the margarite from Chester and find its 



composition as follows: 



Silica 32.21 



Alumina 48.87 



Lime 10.02 



Oxide of iron 2.50 



Manganese 20 



Magnesia 32 



Soda and little potash 1.91 



Lithia 32 



Water 4.61 



There is a little titanic acid with the oxide of iron that I 

 did not estimate. 



Chlorite. — This mineral as found with the emery is the so- 

 called corundophilite of Shepard. On examination it proves to 

 be, both chemically and physically, a chlorite of the variety 

 ripidolite. 



Biotite. — In examining a specimen of dark-green micaceous 

 mineral which I took to be chlorite (the corundophilite of 



