L58 Smyth, Jr. — New Locality of Pyrrhotite Crystals 



their geological relationships are somewhat different. Pyrrho- 

 tite is essentially a mineral of the igneous and metainorphic 

 rocks, and to some extent of metalliferous veins, while pyrite 

 though occurring in all of these associations is also widespread 

 in the sedimentary rocks. 



Lacroix* gives live modes of occurrence for pyrrhotite : in 

 eruptive rocks; in contact-metamorphosed sediments; in 

 meteorites ; in metalliferous veins ; and in crystalline schists ; 

 the normal sediments not appearing at all in the list. This 

 latter type of occurrence is represented by the instance under 

 consideration, which is thus somewhat exceptional. Of course, 

 there is a certain similarity between the secondary cavities lined 

 with minerals deposited from solution and the true metallifer- 

 ous veins, and it is with the latter class of occurrences that the 

 pyrrhotite here described has more in common. Nevertheless, 

 the conditions represented in the Clinton rocks, though lead- 

 ing to a considerable rearrangement of constituents, are very 

 different from those associated with the formation of typical 

 metalliferous veins, with their high temperatures and pressures, 

 and immensely potent chemical agents. To place the present 

 occurrence of pyrrhotite with the metalliferous veins would be 

 wholly unjustifiable, its proper classification being in associa- 

 tion with sedimentary rocks, corresponding to Lacroix'sf fourth 

 mode of occurrence for pyrite. 



The finding of these crystals recalled a similar occurrence 

 noted many years ago, but never recorded, and of which but 

 one specimen is at hand. The locality is Clinton, 1ST. Y., some 

 four miles east of the one described above, and the horizon is 

 the oolitic iron ore, about twenty feet below the fossil ore of 

 the preceding locality. In this oolitic ore a few small cavities 

 lined with pyrrhotite have been found. The mineral is in 

 very thin hexagonal plates, resembling closely the third habit 

 described above, with a dark-bronze, or tarnished surface. 

 The ci'ystals are always small, hardly exceeding a millimeter 

 in diameter and are implanted upon the edges. As a further 

 instance of crystallized pyrrhotite in sedimentary rocks they 

 are of interest, though of little consequence as specimens of 

 the mineral. 



Here again there is a complete absence of evidence as to 

 why pyrrhotite was formed instead of pyrite, which occurs in 

 much greater quantity, though not found thus far in direct 

 association with the pyrrhotite. 



Pseudomorphs. 



The alteration of pyrrhotite to limonite mentioned above 

 runs all the way from a slight superficial change to complete 

 *Min. de la France, II, pt. 2, p. 564. flbid, P- 578. 



