ORES AND MINERALS ASSOCIATED WITH TIIK GOLD. 



365 



The Geological Survey having, however, done little work in the platiniferous 

 region, the writer has no original information of special value to offer on this 

 subject. It is certain that the metals in question occur in the northern part 

 of the State in considerable abundance, and it is not positively known that 

 they have been found at all in the central and southern counties. The 

 practically important ores of this group occurring in northern California are 

 two: native platinum, which is an alloy of this metal with iridium, rhodium, 

 palladium, etc. ; and iridosmine, a mixture of the two metals, iridium and 

 osmium, in varying proportions. Besides these, there are laurite, a sul- 

 phuret of osmium and ruthenium ; and, according to Dr. Genth, probably 

 platin-iridium, a combination of platinum and iridium in different proportions. 

 Laurite (named in honor of Mrs. Laura Joy) was first discovered by Wohler 

 in the platinum washings of Borneo, and afterwards found by him, in con- 

 nection with platinum, gold, chromic iron, zircon, quartz, and microscopic 

 diamonds, in washings from the coast of Oregon ; and the same mineral, in 

 all probability, exists in northern California. 



Native platinum and iridosmine occur together in the beach-sands from 

 Cape Blanco to Cape Mendocino, as also at Cherokee Flat in Butte County. 

 Of the quantity of these two mineral species obtained, or of their relative 

 amount, no definite statement can be given.* According to Professor Pettee, 



the occurrence of platinum in the sands in the vicinity of Oroville, has 

 attracted the attention of Mr. Edison, avIio last year was engaged in erecting 

 works at that place for saving this valuable material. 



The following analyses (by Sainte Claire Dcville and H. Debray) seem to 

 be the only complete analyses ever made of the California platinum. f 



* The following information in reference to California iridosmine was communicated to Dr. Gibbs by the 



officers of the United States Assay OHiee, at New York : "For the first year or two after the establishment of the 

 United States Assay Office, the proportion of osmiridiuin in the California gold did not exceed half an ounce 

 to the million of dollars. Afterward, the proportion increased till the average was seven or eight ounces to 

 the million of gold. Then for a, year or more the quantity diminished, hut for the last year it lias been as 

 large as ever. These differences depend on the variable composition of the native gold and the constant dis- 

 rovery of new diggings. The grains of osmiridinm, suitable for pens, are roundish and solid, not liable to 

 exfoliate when struck or heated. They seem to have a different composition from the compressed and tabular 

 crystals. The proportion of them is usually more than a tenth of all the alloy, but it is sometimes as large 

 as one fifth. The carefully selected grains used by the gold-pen makers are so minute that from 10,000 to 

 15,000 of them are contained in a single ounce. The very best are worth at least $250 an ounce, and a cubic 

 inch, which would be equal to about eleven ounces, is worth $2,750. Am. Jour. Sci. (2) XXXI. p. 63. 

 t Ann. de Chiniie et de Physique (3) LVI. p. 449. 









