\6 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



of silver to the metal and melt the mixture, and then allow the melt to 

 stand some time. The grains of iridosmine do not alloy with the gold 

 and silver, and being very heavy they settle to the bottom of the cru- 

 cible. By carefully pouring off the top of the melt the iridosmine re- 

 mains behind, with some silver and a little gold. The other metals are 

 afterwards dissolved by acids, leaving the iridosmine. 



By fusing iridosmine with phosphorus and treating the fused mass 

 with lime at a high heat a nearly pure iridium is obtained, and this is 

 finding application for purposes where resistance to corrosive influ- 

 ences is required. A small amount of oxide of iridium is used as a 

 black color in decorating j)ottery. 



To illustrate iridosmine seven specimens are shown. Four specimens 

 from Randolph, Coos County, Oregon, represent the occurrence and as- 

 sociates of iridosmine. 



(1) Sand, showing the material in which the gold and iridosmine are fonud. 

 (64749.) 



(2) Gold dust, containing a few flakes of iridosmine, together with some heavy 

 material; obtained by washing the sand. (64747.) 



(3) Iridosmine, in scales and dust, separated from tlie gold ; contains a small amount, 

 of platinum. (44296.) 



(4) Black sand, consisting of various heavy minerals, especially magnetite, pyrite, 

 zircon, cassiterite, and garnet, that collect with the metal in the washing operation. 

 (6474H.) 



(5) Iridosmine, selected coarse scales, suitable for making peu points. California. 

 (5.5407.) 



(6) Iridosmiue, selected line scales, suitable for making pen points. California. 

 (55406.) 



(7) Iridosmine, separated from placer gold at the United States Mint, by fusing the 

 gold with silver. (54971.) 



SILVER. 



Silver Minerals, 



silver. (wire silver.) 



Composition : Ag. Silver, generally containing a little gold and 

 copper, and frequently other metals in very small amounts. 



Silver crystallizes in the isometric system, especially in cubes and 

 octahedrons, and in combinations of these. Crystals are frequently 

 very much distorted, while compound and twin crystals are very com- 

 mon. Its most frequent occurrence is in the form of wires from ^ inch 

 in diameter down to hair-like and mossy masses, which are generally 

 distorted octahedrons. It frequently occurs in arborescent or tree-like 

 forms in which the branching takes place at sixty or ninety degrees, 

 which are likewise distorted crystals. It also occurs in superficial coat- 

 ings, crystallized and uncrystallized, and massive. Masses of several 

 hundred weight have been found a number of times, and one mass at 

 Sonora, Mexico, was said to weigh 2,700 pounds. 



