202 Decomposition of Iron Pyrites. 



No. 112. Marcasitic pyrite. London, England. A fine 

 grayish laminated clay, with pyritiferons, shining, bronze- 

 colored films over many planes of lamination. Some of these 

 surfaces are drusy with microscopic octahedra and with spher- 

 ules roughened by the projecting apices of crystals of pyrite. 

 The surfaces abound in diatomaceous forms of many species 

 (already described by Shrubsole, Kitton, and others), converted 

 into pyrite, bronze-colored without, grayish white and splendent 

 on fresh fracture. From the London Clay. Decomposition : this 

 begins with a golden yellow to bronze-colored tarnish, passing 

 into a reddish film, and ending by hepatic alteration into red- 

 dish brown turgite -ochre. (See also further description in 

 paper in Jour. N. Y., Micr. Society, 1886, p. 11). 



No. 113. Pyrite. Victoria Gold Hill, Colorado. Very fine- 

 grained seams of yellowish auriferous pyrite ; pale brass-yellow, 

 splendent, and conchoidal on fracture ; imbedded in and inti- 

 mately mixed with white quartz, particles of which, together 

 with botryoidal opal and purple fluorite in geodes, were distin- 

 guished under the microscope in the grains used for determina- 

 tion of density. Imperfect microscopic cubes of pyrite were also 

 seen. Deco7nposition : dull yellow tarnish in part. 



No. 114. Pyrite. Antbony's Nose, above Peekskill, New 

 York. A fine-grained yellowish veinstone, whose particles ap- 

 pear grayish white to light brass-yellow, splendent, and con- 

 choidal on fracture. The material is soft to the knife, with 

 gray streak, but not homogeneous. Under a loup, abundant 

 vari-colored specks are seen : pyrite in irregular particles, 

 white quartz, pyrrhotite, chalcopyrite, and scattered prisms of 

 apatite with rounded ends. Under a microscope, imperfect, flat- 

 tened, and polished cubes of pyrite were distinguished, modified 

 by the pyritohedron and sometimes striated. This ore has been 

 often described as pyrrhotite. Decomposition : with the excep- 

 tion of a common yellow and orange tarnish, sometimes irides- 

 cent, little alteration is seen in this specimen, a freshly extract- 

 ed ore, without surface of weathering. 



No. 115. Pyrite. Lake Memphremagog, Maine. A fine- 

 granular, compact, but not homogeneous ore, mottled and 

 streaked with brass-yellow and bronze-yellow or gray, soft to 

 the knife with gray streak, and consisting largely of pyrite and 



