C. H. Behre, Jr. — Native Antimony. 333 



that the replacement veinlets frequently curve around 

 areas of the lighter-colored valentinite. Closely spaced 

 replacements of the black by this tissure-filling mineral 

 are especially common. 



This translucent, vein-forming mineral is locally 

 bordered by a substance that is still lighter under the 

 reflecting microscope but composes areas too small for 

 microchemical or pyrognostic study. Frequently this 

 lighter-colored mineral fills an entire veinlet and seems to 

 be an intermediate product between the associated darker 

 stibiconite and those more nearly anhydrous oxides that 

 immediately border the vein. Possibly it may be crys- 

 talline, though generally amorphous, as a few similarly 

 colored crystals have been observed microscopically in 

 narrow veins. 



Quartz is found here and there in the replacement 

 veinlets, where it is apparently contemporaneous with 

 valentinite and the black mineral, and in the coating of the 

 nodules. It is nowhere of the same age as the native 

 metal. 



The general relations of these various compounds of 

 antimony demonstrate that the pure metal has altered per- 

 ipherally and along fissures, probably partially through 

 the action of oxygenated waters, to valentinite and a 

 distinct mineral of generally similar chemical composition 

 but black in color and differing in microchemical reac- 

 tions. This alteration has been slow enough to permit 

 the formation of replacement and fissure veinlets of the 

 same minerals, especially of valentinite, by circulating 

 solutions. Subsequently valentinite and the black min- 

 eral have been replaced (altered) by another mineral and 

 its intermediate, which are presumably more hydrated 

 exides of antimony, — possibly stibiconite and ^' white 

 antimony ocher.^' This last replacement and fissure 

 filling are recorded by the veinlets of megascopically 

 translucent, microscopically gray mineral. Of the origin 

 of the native antimony itself, unfortunately no clue is 

 afforded. 



University of Chicago, 

 September 13, 1921. 



