GEOLOGY IN NATIONAL MUSEUM — MERRILL. 297 



used largely in the manufacture of carbons for electric lights and 

 for imparting desired tints to porcelain, and to some extent in the 

 manufacture of steel. 



Iron ores are displayed in two American cases showing in form of 

 hand specimens all the varieties produced within the limits of the 

 United States. In the wall case extending along the north and east 

 sides of the Range are ores of like nature, but in many cases in larger 

 form, from the principal iron producing localities of the world. 

 Adjacent to this collection is a desk top case against the east window 

 showing the origin of limonite iron ore through the oxidation of 

 iron pyrite and pyrrholite. Another case of similar pattern contains 

 a small collection consisting of weighed samples of various ores each 

 accompanied by the porportional amount of its essential constituents. 

 The collection includes (1) ores of copper in form of chalcopyrite, 

 (2) zinc in form of sphalerite, (3) lead in form of galena, (4) tin 

 in form of cassiterite, and (5) iron in form of magnetite, hematite, 

 and limonite. 



The nonmetallic series begins with the American cases on the west 

 side of the hall immediately adjoining the mineral collections. On 

 account of its close relationship with the gem collections, an exhibit 

 of rocks and associated minerals from the diamond mines of South 

 Africa is given first place. This collection was donated to the Mu- 

 seum by Mr. Gardner F. Williams and is described in the catalogue 

 of the Gem collection (Bull. 118, U.S.N.M.). 



Under the term asbestos, the commercial world includes sev- 

 eral mineral species differing in origin and chemical composition, 

 but alike in possessing a fibrous structure which adapts them to 

 sundry commercial purposes. Of these the mineral chrysotile (ami- 

 anthus), a fibrous form of the mineral serpentine, is by far the most 

 generally used, both on account of its abundance and the softness 

 and pliability of its fibers which permits of their being woven and 

 used in fireproof fabrics. The smaller samples shown in the Amer- 

 ican case adjacent to that just described are supplemented by the 

 larger ones from Canada (pi. 19) and Vermont. Of exceptional 

 beauty are the golden yellow varieties from the Grand Canyon 

 region in Arizona. The South African crocidolite and amesite, 

 though closely resembling chrysotile in structure, are of quite dif- 

 ference composition; they are, however, used for similar purposes. 

 The amphibolic asbestos, tremolite and anthophyllite, differ from 

 those described in having a less pliable fiber. They are therefore used 

 mainly in the manufacture of felts and packing materials. They 

 occur mainly associated with the metamorphic schists. 



The asbestos exhibit is succeeded by one including the minerals 

 known under the name of talc, or steatite, and pyrophyllite. These 



