384 



DESCRIPTIVE MINERALOGY. 



Composition. It consists entirely of iron and oxygen, in the proportion of two atoms of 

 peroxide to one atom of protoxide, and contains 28.21 of oxygen and 71 .79 of metallic iron. 

 But these proportions are liable to variation. The true formula is probably Fe04-Fea03.* 



Geological Situation. This mineral, which occurs in beds, veins and masses of vast 

 extent, is found only in the older formations, as granite, gneiss and mica slate. It has also 

 been found in the transition and secondary trap rocks, but we have as yet no instances of the 

 kind in this State. 



localities. 



In the former part of this work (p. 5), I have given a full account of our localities of mag- 

 netic iron ore, with the modes of reduction practised in various parts of the State (p. 38). I 

 shall therefore here only introduce a few notices which may be interesting in a strictly mine- 

 ralogical point of view. 



'^'  The finest crystal of the magnetic oxide of iron which I have seen 



from this State, is in the cabinet of the Albany Institute, and was 

 presented to it many years since by Teunis Van Vechten, Esq. of 

 Albany. It is said to have been found in Essex county. The form 

 is a cuneiform octahedron, similar to Fig. 438, but with some of the 

 edges truncated. It is an inch and a half in length, and is strongly 

 magnetic, but feebly polar. 



O'Neil mine in the county of Orange, has been long known as one of the most interesting 

 localities of the crystallized variety of the magnetic iron ore. In the fissures of the massive 

 variety, crystals of small size, but very perfect, have been found in abundance. They are 

 black and shining, but often have a beautiful iridescence. The most common forms are the 

 regular octahedron. Fig. 437 ; the octahedron with one or more of the solid angles replaced 

 by tangent planes, as in Figs. 439 and 440. These replacements are, in a few cases, carried 

 so far as to give rise to the form Fig. 441, and even the cube 442 ; but the latter is very rare 



Fig. 439. 



Fig. 440. 



Fig. 441. 



Fig. 442. 



* There is still a difference of opinion, however, in regard to the true chemical formula of this ore. 



