222 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



as well as irregular areas and in many places lias been partially re- 

 placed by quartz. This replacement results in the usual hackly 

 gangue quartz. The associated gangue minerals are quartz, chal- 

 cedony, and some opal. 31 



OWYHEE COUNTY 



As described under quartz, much of the ore of the De Lamar and 

 other mines of the Silver City region is characterized by what is 

 called lamellar, hackly, or pseudomorphous quartz. This is prob- 

 ably in all cases secondary after calcite of the argentine variety. 

 The scarcity of calcite in the veins at present is noteworthy and only 

 a very few specimens have been found showing any of the argentine 

 not yet replaced. A single specimen collected by Lindgren consists 

 of thick plates of calcite tabular to the basal pinacoid and arranged 

 in cellular aggregates having exactly the structure of much of the 

 platy quartz. Calcite occurs also in a specimen from a tunnel dump 

 on the south side of Long Gulch below the Blaine tunnel. This 

 specimen consists of brecciated basalt fragments surrounded by mas- 

 sive yellow-green epidote. The interstices of the breccia are lined 

 with brilliant quartz crystals stained bright yellow at their bases. 

 The latest deposit in the cavities is the calcite in thin white lamellar 

 plates with pearly luster. 



DOLOMITE (271) 

 Calcium-magnesium carbonate, CaC0 3 .MgC03. Rhombohedral. 



Dolomite, the double carbonate of lime and magnesia occurs 

 both as a vein mineral and as bedded formations constituting dolomi- 

 tic limestone and marble. Accurate identification of the mineral in 

 veins, as distinct from other similar carbonates, usually requires 

 analysis and identifications based upon superficial characters are 

 only tentative. The following occurrences probably are but a small 

 part of those in the State. 



BEAR LAKE COUNTY 



At the Blackstone mine in the Bear River Range crystalline gray 

 dolomite forms the gangue of lead ores in limestone. 32 



BLAINE COUNTY 



Dolomite probably occurs with other carbonates in a number of 

 the mines of the Wood River district. A specimen from the North 

 Star mine consists of a granular pale buff to cream colored carbonate 

 inclosing black sphalerite and prismatic crystals of arsenopyrite. 

 Small cavities are lined with curved rhombohedral crystals of the 

 carbonate which is probably an iron bearing dolomite. 



3 > J. B. Umpleby. U. S. Geol. Survey, Bull. 539, p. 85, 1913. 

 32 R. W. Richards. U. S. Geol. Survey, Bull. 470, p. 182, 1911. 



