220 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



Small druses of crystals having this same flat rhombohedral 

 habit have also been found in cracks in basic dikes at several places 

 in the district. Such crystals were especially noted in the lampro- 

 phyric dike cut by the portal of the Lombardy tunnel in Italian 

 Gulch north of Kellogg and in the large altered dike intersected by 

 the Kellogg (No. 9) level of the Bunker Hill mine near the point 

 where the tunnel crosses the Osburn fault. 



In the Evolution prospect on the north side of the river, between 

 Big Creek and Osburn, a large vein of solid calcite of a blue-gray to 

 white or buff color is in places 30 feet wide. Numerous other occur- 

 rences of ordinary calcite have been observed. It seems probable 

 that some of the massive carbonates which occur as gangue minerals, 

 especially in the copper prospects in the Wallace and Prichard for- 

 mations around the edges of the Coeur d' Alene district, which weather 

 to a brown color and heretofore have been called siderite, are slightly 

 ferriferous calcite. A specimen labeled " Black Bear Prospect, 

 Taft Quadrangle," consists of coarse cleavage surfaces up to 4 cm. in 

 diameter, of a buff-weathering white carbonate cut by later seams of 

 chlorite, quartz, and chalcopyrite. The carbonate, upon analysis, 

 gave the following results: 



Analysis of calcite, Black Bear prospect 



(E. V. Shannon, analyst.) 



Per cent 



Insoluble (quartz) 0. 40 



Calcium carbonate (CaC0 3 ) 96. 22 



Magnesium carbonate (MgCO-3) . 56 



Iron carbonate (FeC0 3 ) 1. 86 



Manganese Carbonate (MnC0 3 ) 1. 05 



Total 100. 09 



This analysis indicates that less than 3 per cent of iron and manganese 

 carbonates in a calcite will cause the mineral to assume a distinctly 

 brown color on weathering. 



CALCITE, variety ARGENTINE 



Although ordinarily calcite is characterized by a rhombohedral 

 habit and the basal pinacoid (0001) occurs but rarely as a small 

 and dull face, a variety of this carbonate of lime having a tabular 

 or lamellar structure and made up of thin plates tabular to the basal 

 pinacoid is known and has been described under the varietal name 

 argentine. Argentine has been found at a number of places in Idaho 

 and is of especial interest since the lamellar structure which character- 

 izes much of the quartz of the Tertiary precious-metal veins is prob- 

 ably pseudomorphous after this variety of calcite. The following 

 occurrences of calcite of the argentine habit have been observed. 



