MINERALOGY. (393 



quite a common vein-mineral and occurs in globular and cockscomb shapes. It is abund- 

 ant in the New Diggings district. It is difficult to preserve specimens of this mineral 

 longer than a few months. 



, Chalcopyrite. Composition: copper S4.6; iron, 30.5; sulphur 34.9. This is tha 

 principal ore of copper in the Lead region, and is most abundantly found in the vicinity 

 of Mineral Point. It usually occurs massive, frequently mixed with pyrite; small and 

 indistinct crystals are occasionally found. 



Hematite. Composition: iron, 70; oxygen, 30. Impure arenaceous varieties of this 

 mineral frequently occur, nowhere, however, sufficiently rich or abundant to be of any 

 economic value. It seems to be chiefly due to the decomposition of pyrite, and is most 

 common as the ferruginous sandstone concretions in the upper beds of the St. Peters. 

 It is also frequently found as ooher, with otlier >ein-minerals, especially in the flat 

 openings. 



Oxide of Manganese. A substance consisting of oxide of manganese with a little 

 oxide of iron, zinc, and traces of magnesia according to an analysis of Dr. Bode of Mil- 

 waukee, is found in crevices in the Trenton limestone, in some diggings situated on 

 Sec. 11, T. 4, R. 1 E. The mineral is as light as cork, color brownish-black, submstallic 

 luster and streak, soUs readily, and is infusiljle. It is very soft, and does not occur 

 crystallized. It has a structure in thin parallel layers resembling wood. 



Calamine. Composition: sUica, 25.0; oxide of zinc, 67.5; water, 7.5. This mineral 

 is of very rare occurrence in the Lead region. It is found in small, drusy crystals, 

 coating Smithsonito. The crystals are very brittle, colorless, and have a vitreous lustre. 

 It is found near Mineral Point. 



Barite. Composition: sulphuric acid, 34.33; baryta, 65.67. It occurs usually white 

 and massive, but sometimes in lamellar and crested forms. The only place where it 

 was found in distinct crystals was in the railroad cut at Scales Mound, where it occurs 

 in small cavities, as small but very perfect transparent crystals, aasociated with dolo- 

 mite and pyrite. It is not a very abundant mineral, but is found in several of the min- 

 ing districts, especially DodgeviRe and Mineral Point. The following is an analysis by 

 Mr. E. T. Sweet, of a specimen from the S. W. qr. of Sec. 6, T. 5, R. 3 E., on Van 

 Meter's survey: 



SiUca 2 . 24 



Alumina - ■ 83 



Sesquioxide of iron 77 



Water Trace. 



Barite, sulphate 95.27 



Lime, sulphate 1 .30 



100.41 



Anglesite. Composition: sulphuric acid 26.4; oxide of lead 73.6. Traces of this 

 mineral are reported as occurring in some of the mining districts, but no specimens 

 have as yet been obtained. It probably originates from the decomposition of galenite. 



Calcite. Composition: carbonic acid 44; lime, 56. This is a vein-mineral common 

 to aU the deposits of ore whether in crevices or openings. It occurs orystalUzed in modified 

 rhombohedrons and scalenohedrons. The variety known as Dog-tooth-spar is a very 

 ■frequent form, especially in the ShuUsburg and Linden districts wliich affords very hand- 

 some cabinet specimens. The Mineral Point district affords handsome rhombohedrons, 

 and the Linden mine affords handsome twin crystals of calcite set on sphalerite (blende). 

 It also occurs there, rarely, as a pseudomorph after marcasite and has then a radiate or 

 divergent form. 



Dolomite. Bitter Spar or Brown Spar. Composition: carbonate of lime and car- 



