THE CHICAGO ACADEMY OF SCIENCES. 



Sphalerite. ZnS. Regular. 



Far more common than either of the above named sulphides 

 is the zinc sulphide in this region. Like galena, it occurs in both 

 the transported crystallines and in the local limestone. The 

 planes most commonly seen are those of the tetrahedron, which 

 are striated, distorted, twinned. 



The coarse, granular masses exhibit good dodekahedral 

 cleavage. The fracture, which is splintery, is little in evidence. 

 The mineral is brittle, has a hardness of 3.5, a specific gravity 

 of 4, and the following colors: yellow, brown, black. Its 

 lustre is resinous, its streak yellowish brown. Before the blow- 

 pipe it fuses with difficulty, giving off sulphur fumes and coat- 

 ing charcoal with a white incrustation of zinc. It dissolves in 

 hydrochloric acid. 



flillerite. NiS. Hexagonal. 



In some of the sphalerite enclosed in chert appear long 

 slender metallic yellow needles, which give under the blow- 

 pipe reactions for nickel. These yellow crystals are millerite. 

 Dana, Naumann,and Lacroix record the association of millerite 

 with calcite, dolomite, fluorite, siderite, pyrite, hematite, with 

 cobalt and silver ores ancj with quartz. No mention is made of 

 its occurrence with sphalerite in any literature upon the sub- 

 ject. This seems to be a new occurrence. The hexagonal 

 needles are often so fine as to justify the name of u Haarkies." 

 Often they are tufted and in confused masses. Cleavage has 

 not been observed. They are brittle, have a hardness of 3.5, 

 and specific gravity of 5.5. Brass to bronze yellow, often with 

 grey iridescent tarnish. The color of the streak is greenish 

 black. To test for nickel, following the method given by 

 Bunsen (See Determinative Mineralogy and Blowpipe Analy- 

 sis, p. 97), I boiled some powdered mineral with nitric acid till 

 dissolved and about 5 c.c. of acid remained. Added water, 

 boiled, poured in excess of ammonia, and filtered. Added 

 caustic potash till ammonia odor was no longer perceptible. 

 The precipitate, hydroxide of nickel, washed in hot water, 

 then treated with borax in oxidizing flame, yielded a bead vio- 

 let colored while hot, and reddish brown when cool. The 

 presence of cobalt was not detected. Millerite is one of the 

 rarest of Cook County minerals. 



More abundant than any of the ten mineral species thus 

 far described is: 



