1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 120 



the eye alone or with the pocket lens, as in the case of the jadeite beads 

 from Mexico. Professor Arzruni,* however, has shown that nephrite 

 is not in all cases an original mineral, but in some instances results 

 from a molecular re-arrangement or uralitization of a mineral of the py- 

 roxene group. He, therefore, very appropriately divides them into the 

 primary nephrites and pyroxene nephrites. H. Traubet has shown, too, 

 that a poition of the nephrite from Jordansmiihl in Silesia is secondary ; 

 as is also that of Keichenstein, the latter resulting from the molecular 

 alteration of diopside.f 



Beck and Muschketow§ too, it will be remembered, considered the 

 asbestus fibers in the Bustraja nephrite as secondary, and noted the 

 presence of still unaltered granules of diopside in the nephrite from 

 Samarkand and Turkestan. It would therefore appear that the true 

 nephrite may grade into a granular diopside rock resembling jadeite, and 

 that therefore the purely macroscopic method suggested can not in all 

 cases be relied upon implicitly. A safer, and indeed the only practical, 

 means of distinguishing between the two substances under the circum- 

 stances noted above would seem to be by their specific gravities, the 

 jadeites varying from 3.01 to 3.32, while the nephrites rarely reach a 

 density of 3.00. 



As regards the possibility of distinguishing by means of thin sections 

 and the microscope between nephrites from various sources. A major- 

 ity of the authorities consulted (and among them are those who have 

 devoted much time to the subject and who having critically examined a 

 large number of slides are capable of rendering opinions of value) appear 

 to favor the view that this is practicable. As for ourselves, with our 

 present experience, we confess to a feeling of skepticism. The presence 

 or absence of inclosures of diopside, magnetite, or ferruginous oxides, 

 the condition of these oxides, whether as ferric or ferrous, the varying 

 tufted, bent, confused fibrous and even granular condition of the consti- 

 tuent parts, are all, together with the color variations and other struct- 

 ural peculiarities, matters of two slight import to be of weight from a 

 petrographic stand-point. If, as seems possible, the majority of the 

 nephrites are of secondary origin, why may we not expect to find all, or 

 at least a great variety, of the structures described in the same or closely 

 adjacent rock masses 1 Chemical analyses on samples from near-lying, 

 or even the same, localities are found often to vary as greatly as those 

 from localities widely separated. Why may we not expect the sam e 

 structural variations when once they are carefully looked for? To our 

 own minds sufficient assurances that the widely scattered jadeite and 

 nephrite objects were derived from many independent sources and pos- 



* Zeit. flir Ethnologie, 1884, p. 300, 



tNeues Jahrb. f. Minn., etc. Beilage Band in, 2. Heft, 1884, p. 417. 



t Neues Jahrb. f. Minn., 1887, n B., 2 Heft, p. 275. The alteration is accompanied 

 ■with a diminution in the amount of lime ; the diopside yielding 21.41 per cent, and 

 the tremolite (nephrite) 11.16 per cent. 



$ Op. at. 



Proc. N. M. 88 9 fycu^tf&i' 



