ART. 21 MIARGYRITE SILVER ORE FROM CALIFORNIA — SHANNON 6 



quartz crystals in these vugs that the best crystals of miargyrite 

 are found, although other less perfect crystals line the \ ugs in massive 

 miargyrite. Hulin notes that small amoimts of arsenopyrite, pyrite 

 pyrargyrite, proustite, chalcopyrite, argentiferous bornite, and 

 stibnite also occur in the ore, but in the specimens at hand these 

 minerals are not conspicuous and do not present any features worthy 

 of special note. Green chromiferous mica is reported to occur 

 rarely in altered wall rock in the outcrop of the Footwall vein. 



The paragenesis of the minerals has been discussed in detail by 

 Hulin. The stylotypite (?) is in part contemporaneous with quartz 

 and is older than miargyrite, which sometimes replaces it. The order 

 of genesis of the several minerals is given as: 



A. Primary: 



1. Silica (chalcedony and quartz). 



2. Pyrite. 



3. Arsenopyrite. 



4. Stylotypite. 



5. Chalcopyrite. 



6. Argentiferous bornite. 



7. Miargyrite. 



8. Pyrargyrite. 



9. Proustite. 



10. Stibnite. 



11. Calcite. 



B. Secondary: 



12. Secondary sulphides. 



13. Cerargyrite. 



14. Melanterite. 



The following metallographic properties and reactions which are 

 obtained on polished sections of the miargyrite are the characteristic 

 ones for the species: 



Color in section: Gray with red internal reflections in places. 



Anisotropism: Strong. 



Color in powder: Dark ruby red, distinctly darker than pyrargyrite. 



1:1 HNO3: Negative. 



1:1 HCl: Fumes tarnish; in places negative. 



20 per cent KCN: Slowly stains brown. 



20 per cent FeCls: Negative. 



40 per cent KOH : Stains iridescent. 



5 per cent HgCh: Negative. 



Since it was not desired to sacrifice the well-crystallized specimens 

 by removing crystals enough to analyze, the analyzed material was 

 taken from a coarse-grained massive specimen. (Cat. U.S.N.M. No. 

 95334.) By boring shallow pits in the centers of large and pure grains 

 of miargyrite on polished surfaces 0.2 gram of pure sample was 

 obtained. This was analyzed in the Museum laboratory with the 

 following results: 



