146 Decomi)osit\on of Ii-on Pyrites. 



of the crystal-faces. The fractured edges of these exhibited, 

 alternating brown and white lines, evidently the edges of alter- 

 nating films of red iron-oxide and of white gypsum. On other 

 octahedra of pyrite, less deeply attacked by oxidation, the red- 

 dish brown coating, about 0.1 mm. in depth, was observed to 

 be sprinkled with little particles and short needles of white vit- 

 riol. Their identity was sufficiently established by putting such 

 a crystal in a drop of water on a slide, with a drop of potassium 

 ferrocyanide in close juxta])osition, and connecting the two 

 drops by means of a wire, while under observation, when the 

 blue precipitate was formed which indicated the presence of a 

 soluble iron-salt. The observation was one of interest, in sug- 

 gesting that the slow oxidation, which results in the formation 

 of a crust of iron-oxide, differs in no way from that which pro- 

 duces the efflorescence of white copperas, in other materials, ex- 

 cept in the further complete oxidation of the iron protoxide. 

 It may also be again suggested that the presence of organic mat- 

 ter, as dust or in solution, must result in the final deoxidation 

 of the sulphuric acid set free in this decomposition, with its es- 

 cape as hydrogen sulphide, or sometimes a partial deposit in the 

 form of free sulphur. 



Pyrite,from Lee, Mass. Thin flai<es of the white dolomitic 

 marble from Lee, containing pyritous particles in an active state 

 of decay. These were chipped from the surface of fragments 

 thrown aside from the construction of the Cathedral at Madison 

 Avenue and Fiftieth Street in New York City, which had been 

 lying exposed to the weather for a few months. Each rusty parti- 

 cle was surrounded by a reddish-brown ochreous film, penetrating 

 the marble irregularly in every direction, sometimes to a dis- 

 tance of one or two centimeters from the decaying particle. 

 The instability and consequent discoloi-ation were so marked, as 

 to suggest the possibility that these particles might consist of 

 marcasite. To determine their true nature, five pounds of the 

 stone were dissolved in weak hydrochloric acid, and the insolu- 

 ble residue was found to consist of angular grains of white 

 quartz, scales of red and colorless phlogopite, and the pyrites, 

 with a small quantity of imperfect prisms of brown and black 

 tourmaline, white tremolite in acicular granules, and bent rods 

 of black rutile. The pyritous grains presented ordinary fori^s 



