Decomposition of Iron Pyrites. 195 



splendent, and sometimes conclioidal on fracture of some grains. 

 On the edges of the specimen, sharp, brilliant, and unmodified 

 cubes were distinguished. Imbedded in a grayish hydromica- 

 schist. Decomposition : a yellow iridescent tarnish. 



Nodule. Freiberg, Saxony. A yellowish gray flattened nod- 

 ule, penetrated by many cracks ; these show that it consists of a 

 finely laminated outer crust of very fine-grained pyrite, coated 

 with glittering cubes, while within appears a finely granular 

 nucleus. 



No. 78. (Outer coat). Pyrite. Yellowish cubes, rarely 

 elongated, and sometimes with solid angles modified by small oc- 

 tahedral planes : fracture, pale brass-yellow, splendent and 

 conclioidal. Decomposition : a yellowish gray tarnish. 



No. 79. .(Inner core). Marcasitic pyrite. A fine grained 

 mixture of particles of pyrite and of nearly the same amount of 

 white quartz. Decomposition : the interstices of the core are 

 filled by an eiflorescence of white vitriol, whose expansion has 

 cracked the nodule, and which is entirely absent from the outer 

 surface. 



No. 80. Pyrite. Saddle Island, near Cape Malagash, Tatmag 

 Bay, Nova Scotia. A concretionary spherical nodule, with lam- 

 inated structure, very finely granular and cryptocrystalline, pale 

 yellowish white and glittering on fracture. This specimen was 

 reported as probably loosened from a sandstone in place. Under 

 a microscope, its material was found to be itself a pyritiferous 

 sandstone, made up of sub-angular to angular grains of gray and 

 white quai'tz, blood-red ochre, and yellowish white feldspar ; 

 its cement, in much less amount, consisting of pale brass-yellow 

 and splendent pyrite, in delicate strings and films between the 

 grains, forming a bright yellow network over the surface. A 

 few imperfect flattened and striated cubes were also thus distin- 

 guished. Decompoaition: a reddish brown ochreous film colors 

 the outer surface. 



No. 81. Pyrite. Eastbourne, England. A concretionary 

 nodule of sausage-shape, showing at one end a core of fine-grain- 

 ed compact pyrite, pale yellowish white and splendent. Decom- 

 position : a brownish yellow film of limonite-ochre over the 

 outer surface, with here and there minute projecting cubes of 

 turgite. pseudomorphous after pyrite. Beneath this film is a 



