178 LARSEN AND WHERRY: HALLOYSITE FROM COLORADO 



MINERALOGY. — Halloijsite from Colorado? Esper S. Lar- 

 sen, Geological Survey, and Edgar T. Wherry, National 

 Museum. 



In the upper workings of the fluorite mine at Wagon Wheel 

 Gap, Colorado, two amorphous hydrous aluminium silicates 

 have been recognized which agree more or less closely with halloy- 

 site as defined by Dana but differ from one another considerably 

 in water content. One has essentially the composition of kao- 

 linite, but is for the most part sensibly isotropic and has the 

 index of refraction 1.557. It occurs in rather large amount as 



TABLE 1 



Analyses and Theoretical Composition 

 of Halloysite 



1 and 2. Analyses of halloysite. 



3. Average of 1 and 2. 



4. Theoretical for A1 2 3 . 2Si0 2 



TABLE 2 



Loss of Water by 

 Halloysite 2 



2H 2 . 2Aq. 



the matrix in which the mineral creedite is imbedded and has 

 been called "isotropic kaolinite." 3 The other contains more 



1 Published with the permission of the Director of the U. S. Geological Sur- 

 vey and of the Secretary of the Smithsonian Institution. 



2 Lowenstein (Zeit. Anorg. Chem., 63: 88-101. 1909), found that halloysite 

 from Laurium, Greece, lost 21.4 per cent H 2 at 110°-130° or over 97 per cent 

 H2SO4, and 6.2 per cent above 130°, but most halloysites cited by Dana behave 

 like the one here described. 



3 Larsen, Esper S., and Wells, Roger C. >Some minerals from the fluorite- 

 barite vein near Wagon Wheel Gap, Color do. Proc. Nat. Acad. Sci., 2: 360. 1916. 



