12(3 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



aud he suggested that it be considered a distinct species in place of being included 

 as a variety under corundum.' His conclusion would obviously be acquiesced in were 

 it not for the strong resemblance in strine and cleavage between the emery and common 

 corundum, making it impossible for us to separate the substances crystallographically 

 from one another. It would, however, be singular if two minerals differing so widely 

 in their other physical qualities should be specifically identical. 



Nothing like a perfect crystal of emery has yet been found at the mine, but it is 

 quite remarkable that the mineral is here generally coarsely massive or in large 

 separate individuals, often of the size of kernels of Indian corn (maize), whose cleav- 

 age is perfect, and which present on their planes the delicate strire so characteristic 

 of adamantine spar from the Carnatic. The color, moreover, is perfectly uniform, a 

 reddish-brown with a faint coppery luster. Its specific gravity is superior to that of 

 corundum by nearly five-tenths, while its power of abrading, as accurately determined 

 in the Turkish and Grecian varieties by Dr. J. L. Smith, is less than half that of the 

 sapphire, though in all its varieties, and especially that of Chester, its scratching 

 power or true hardness is sufficient to scratch topaz. It is constantly magnetic. 



In chemical composition the Chester emery is equally uniform, and in constitu- 

 tion may be considered strictly isomorphous with the magnetite, which species indeed 

 coexist in the same vein or in closely contiguous ofifshoots therefrom. Supposing 

 alumina to have replaced the peroxide of iron (ferrous acid), we then have instead of 

 ferrite of iron (magnetite), the aluminate of the same base (emery), the chemical 

 expression of the first being Fes', that of the second Fe^. 



The composition of emery in 100 parts, being deduced from this formula, gives a 

 comiiosition scarcely different from the results of actual analysis. Its percentage of 

 metallic iron is therefore a fraction over 29. It hence becomes apparent how natural 

 was the mistake of regarding it as an ore of iron. 



Several varieties of emery at Chester, growing out of the size of particles, their 

 mode of aggregation, and mixture of other minerals require to be jioiuted out. 



(a) Granular emery. — This occurs in flattened grains, from the size of kernels of 

 Indian corn down to that of i>eppercorns, disseminated through coruudophilite. The 

 grains rarely touch each other and are distributed through the rather open green 

 mineral, with their flat faces parallel to the foliation of the gangue. Hence this 

 variety cleaves without difficulty into slaty fragments a few inches in thickness. It 

 also breaks crosswise without much difficulty. The pure emery forms from one-half 

 to three- fifths the bulk of the aggregate. 



(6) Veined emery. — This variety arises from the occasional contact and partial 

 union of the individuals (by their edges mostly) of the preceding variety. The veins 

 are much interrupted and are rarely above half an inch thick. The granular and 

 veined varieties sometimes pass into each other. 



(c) Compact emery. — This variety, though not absolutely compact in the mineral- 

 ogical sense, is nevertheless a very close, finegrained mineral in its structure, the 



' Should it hereafter be found proper to separate emery from corundum the name of enierite might 

 not be an unsuitable designation for the new species. — [Shepard.] 



