MINERAL COLLECTING IN THE ROCKY MOUNTAIN 



STATES 



By E. P. HENDERSON 



Assistant Curator, Division of Physical and Chemical Geology, 



U. S. National Museum 



The field-work of 1932 1 was in cooperation with the department of 

 geology of Harvard University and under the auspices of the Canfield 

 Fund. In June, accompanied by F. A. Gonyer representing Harvard, 

 I left Washington by automobile for the Rocky Mountain States. 

 More than 10,000 miles of territory was covered, and the list of 

 minerals collected or searched for rivals the index of a textbook on 

 mineralogy. 



The first collecting was in the dolomite quarries at Clay Center in 

 northern Ohio, where crystals of celestite and fluorite are found filling 

 cavities in the dolomite. The second stop was at Keokuk, Iowa, a dis- 

 trict widely known for the quartz geodes found in the nearby clay 

 beds. A geode is a rock with a hollow center partly filled with crys- 

 tals, sometimes several different minerals, and it is difficult to under- 

 stand how these different elements passed through the impervious 

 siliceous shell covering. After a few hours of excavating in the clay 

 two large and several small geodes were unearthed, but unfortunately 

 these were damaged in opening them. However, William M. Thomas, 

 a local collecter of geodes, kindly donated his largest geode to the 

 National Museum, a specimen containing a cavity 6 inches in diameter 

 and 18 inches deep completely lined with quartz crystals. 



Our next collecting was at Lead, near the northern edge of the 

 Black Hills of South Dakota, where is located the Homestake mine, 

 the largest gold mine in the LJnited States. Hundreds of individuals 

 work along the nearby rivers in an effort to recover the gold which 

 nature buried among the gravels or concealed by rock slides. 



Turning west, we pushed on to Butte, Mont., named from the 

 prominent hill, geologically known as a butte, on which it is located. 

 This hill, known as the richest hill in the world, produces each year 

 from within a mining area of about 5 miles enormous tonnages of 

 copper, lead, and zinc, besides large quantities of silver and gold. 

 Butte is the home of the Anaconda Copper Co., and the success of my 

 collecting at this place was largely due to the generous cooperation 

 of the company officials. Many mineral specimens were obtained, as 

 well as several large pieces of ore for the exhibit of applied geology. 



