222 ECONOMIC GEOLOGY 



magnetite and diaspore, in association with repidolite and marger- 

 ite, and traversing metamorphics. 



Rubies occur in situ in the limestones of Upper Burma, north 

 of Mandalay, also in the soils upon the adjacent hillsides and in 

 the gem-bearing gravels of the valleys. Gem sapphires are found 

 near Helena, Montana, in the gold washings and in the various 

 bars in the Missouri River. 



Bauxite occurs in pockets or lenses of variable length and 

 breadth (Fig. 117). It may be either pisolitic or clay-like in 

 structure, white or red in color. All of the red varieties are rich 

 in iron. Gibbsite in Arkansas is of the granitic type and rests 

 upon a bed of clay derived from an elaeolite syenite, from which 

 also the gibbsite was probably derived. The alums occur as 

 incrustations and sometimes as stalactites around mineral springs 

 and at the entrance to mines. 



Cryolite occurs in a large bedded deposit in Greenland which 

 F. Johnstrup regards as a concretionary secretion in eruptive 

 granite. Cryolite is found sparingly in the granites of Pikes 

 Peak, Colorado, and at Miask in the Ural Mountains. 



Geographical Distribution. There are many scattered occur- 

 rences of corundum and its associated minerals along the 

 Appalachian belt from Dudley ville, Alabama, to Greenwood, 

 Maine. The mines of the greatest commercial significance are 

 located at Laurel Creek, Georgia, and Corundum Hill, North 

 Carolina. It occurs at Unionville, Pennsylvania, in masses 

 weighing 4,000 Ib. Here it is associated with tourmaline, mar- 

 gerite and albite. The deposits at Chester, Massachusetts, 

 have been operated for a considerable period of time in the manu- 

 facture of the well known Chester emery. Emery, magnetite 

 and diaspore enter into the finished product, under the name of 

 emery. Probably the largest deposits of emery in the world are 

 found on the Island of Naxos in the Grecian Archipelago and in 

 Asia Minor where the ore deposits are supposed to be the prod- 

 uct of metamorphism. 



There are five distinct districts of commercial bauxite in the 

 United States. (1) Wilkinson County, Georgia, district; (2) 

 Georgia- Alabama district; (3) Tennessee district; (4) Arkansas 

 district; and (5) New Mexico district. 



(1) According to A. C. Veatch commercial bauxite occurs in 

 Wilkinson county, Georgia, near the margin of the Coastal Plain. 

 The beds have a maximum thickness of 10 ft. and lie near the con- 



