THE GANGUE MINERALS. 1131 



and thus even the most soluble of the abundant elements have been fixed 

 in the veins to some extent. 



While the silicates are dominantly gangue minerals, silicates of zinc, 

 manganese, and nickel occur as ores. Silicate of zinc occurs both as 

 willemite (2ZnO . Si0 2 ) and as calamine (BLO . 2ZnO . Si0 2 ). The most 

 notable occurrence of willemite is in the New Jersey zinc deposits. In 

 reference to this mineral the question arises whether it was formed as an 

 original precipitate from the deep circulation or was produced by dehydra- 

 tion of calamine in the zone of anamorphism, the calamine having been 

 formed originally in the belt of weathering in the same manner as in the 

 Mississippi Valley. Whether calamine occurs as zinc ore as an original 

 deposit by ascending waters I do not know. The abundant development 

 of calamine in consequence of the reactions of the belt of weathering is 

 very well known, as explained on pages 1144, 1147-1148. 



Manganese silicate occurs rather abundantly as rhodonite (MnO.Si0 2 ). 

 For the most part, however, this is a gangue mineral rather than an ore, its 

 occurrence being well illustrated at Butte, Mont., and in the Smuggler 

 Union mine and other places in the San Juan district, Colorado. Although 

 sometimes found in considerable quantities, it is not now used in the United 

 States as a source of manganese on account of its high percentage of silica. 6 



The most notable occurrence of nickel as a silicate is in New Caledonia. 

 Packard says: "The nickel ore of New Caledonia is a hydrated silicate of 

 nickel and magnesium (garnierite) which occurs intimately associated with 

 serpentine. . . . The field observations showed that the nickel silicate is 

 clearly an alteration product of the serpentine. . . . Hot springs have 

 played a conspicuous part in furthering the decomposition of the nickel- 

 bearing serpentine into garnierite and the other products." ° Packard also 

 notes the occurrence of nickel silicate at Riddles, Oreg., in North Carolina, 

 in the Urals, and in Silesia. In all cases it is a secondary alteration 

 product usually derived from a serpentine which itself was derived from a 

 nickeliferous olivine. From Packard's descriptions it appears probable that 

 the nickel silicate mined is an oxidized product formed by the reaction of 



«Kemp, J. F., The ore deposits at Franklin Furnace and Ogdensburg, New Jersey: Trans. New 

 York Acad. Sci., vol. 13, 1893-94, p. 90. 



b Penrose, R. A. F., jr., Manganese, its uses, ores, and deposits: Ann. Rept. Geol. Survey Arkansas 

 for 1890, vol. 1, 1891, p. 85. 



'-Packard, R. L., Genesis of nickel ores: Mineral Resources, 1893, pp. 170-171. 



