Decomjoosition of Iron Pyrites. 

 ETCHED NUCLEI OF VYmT^.— Continued. 



163 



Col- 





lection 

 No. 



Locality. 



43 



Traversella, Italy, 



46 



Roxbnry, Mass, 



55 



Guanajuato, Mex, 



84 



Hazelton, Pa, 



91 



Mahanoy City, Pa. 



91 



Mahanoy City, Pa. 



96 



Somerville, Mass. 



102 



Scholiarie, N. Y. 



Sp. 

 Gr. 



Etch- 

 ing 

 Agent 



4.985 



Br 



4.985 



NO^ 



4.954 



N02 



4.907 



Br 



4.905 



NO^ 



4.905 



Br 



4.843 



N02 



4.809 



Br 



Characteristics of the 

 Etched Surface. 



Minutely shagreen-like, or mere- 

 ly pitted on some faces. Cracks 

 and cleavage-lines etched out. 



Coarser shagreen-like surface. 

 Spherules often elliptical, 

 sometimes square. Some sur- 

 faces merely pitted. 



Finely granular mass, thorough- 

 ly seamed by very minute 

 clefts. Slight differences in 

 the color and lustre of the 

 granules. 



A minutely spongy, yellowish 

 white and deeply fretted net- 

 work ; the cavities and grains 

 about 4 /.I in diameter. Cleav- 

 age lines marked by the pro- 

 jection of solid brilliant yellow 

 ridges. 



Minutely fretted and pitted like 

 the preceding, with many 

 short furrows, and rarely pro- 

 jecting octahedra. 



Like the preceding. Rarely, a 

 few isolated spherules. 



Coarse grains projecting above 

 a fine grained groundmass. 

 Cleavage-lines etclied out 

 deeply, sometimes producing 

 six-sided grains by crossing. 



Commonly pitted, and furrowed 

 by irregular clefts. Abundant 

 particles of gray quartz inclu- 

 ded, separated by a network of 

 bright pyrite. 



When it is considered that the specimens subjected to the oxi- 

 dizing tests were, in m11 cases, crystals selected for apparent pur- 

 ity, with brilliant faces and generally a strongly marked con- 

 choidal fracture, it will be seen that these peculiarities of etch- 

 ing point to remarkable differences in structure and in latent 

 composition, and to an unexpected lack of homogeneity in 

 most specimens. Of these differences the proofs thus obtained 

 were far more conclusive than those by the ordinary microscopic 

 examination of the natural crystal-faces or fracture-surfaces. 

 The following five varieties of etching were distinguished, and 



