RE-EXAMINATION OF AMERICAN MINERALS. 159 



in this respect resembling that from Zacatecas as analyzed by 

 Bergmann. 



This mineral is found in granite or quartz. It is also asso- 

 ciated with pyromorphite, and sometimes the two run together 

 so as to present no distinct line of demarkation between them ; 

 some of the specimens consist of the two minerals, the pyro- 

 morphite occupying one entire surface, and mimetene the 

 opposite surface, and between various shades of the mixture. 

 It has been found with galena and carbonate of lead. 



54. Galena. 



The compact, fibrous, and crystallized varieties of galena 

 occur at this mine. Fine crystals are found, either a perfect 

 cube, cube with modified edges and angles, octahedron and 

 rhombic dodecahedron often very much flattened out and occa- 

 sionally rounded to an almost globular form ; these rounded 

 crystals are usually covered with pyromorphite. The galena 

 is sometimes cellular, arising from partial decomposition, the 

 exterior portion presenting a black drusy appearance, the inte- 

 rior of a bright steel color; this variety is particularly rich in 

 silver, and also contains crystals of sulphur. 



The galena is argentiferous, giving an average yield of thirty 

 ounces to the ton. It is found associated with quartz, calcite, 

 and fluor-spar, frequently inserted in the crystals of these sub- 

 stances; it is also a common associate of all the minerals of this 

 locality. Some of the cubical crystals have their surfaces partly 

 decomposed and covered with a layer of crystals of carbonate. 

 Specimens are found of very large cubical and octahedral crys- 

 tals, forming slabs several square feet in surface, completely 

 covered with a layer of leek -green phosphate. The cavities 

 of the galena frequently contain sulphur. 



55. Copper. 



Native copper is found only in delicate films on hematite or 

 quartz crystal, and forms an interposing layer between the 

 hematite and copper pyrites. 



56. Copper Pyrites. 



Copper pyrites is found in some cases in sufficient quantity 

 to be worked as an ore ; some of the masses are of considerable 



