376 MR. A. M. EINLAYS0ST ON THE NEPHRITE [Aug. I909, 



and the full explanation must await the discovery and study of the 

 rock in situ. 



Here one can only remark that the original rock was of hartz- 

 bergite or similar type, that the alteration is apparently a deep- 

 seated one, and that the resulting aggregate of fibrous amphibole 

 has all the characters of nephrite, except the foliated and felted 

 structure, which is evidently due to great mechanical stress and 

 pressure. 



Origin of the Nephrite. 



Arzruni divided nephrites, according to their mode of origin, 

 into two classes : — (1) Primary nephrite, and (2) secondary 

 nephrite, or nephrite derived by uralitization of pyroxenes [14]. 



Dr. Dieseldorffs examination of the nephrite of D'Urville Island 

 showed that his specimens were due largely to uralitization of 

 pyroxenes [5, pp. 334 et seqq.~]. 



Traube's work on the nephrite of Jordansmiihl [15] shows the 

 nephrite of that locality to have been formed partly by dynamic 

 metamorphism apparently of serpentine, partly by contact-action on 

 the surrounding granulite, and partly by uralitization of pyroxene. 

 The nephrite of the first mode of origin is of a pale colour, that due 

 to the other two processes is dark green. 



Again, the Reichenstein nephrite has been shown by Traube to be 

 due to the uralitization of diopside [16 | accompanied by a decrease 

 in the percentage of lime from 21-41 per cent, in the diopside to 

 11'16 per cent, in the nephrite. 



The recent investigations of Prof. Iddings, on the Heber R. Bishop 

 collection of jadeite and nephrite, show how widespread is the 

 occurrence of secondary nephrite ; and he has concluded that the 

 uralitization of pyroxenes in general, and of the fibrous species 

 jadeite in particular, is the normal mode of origin of nephrite [12, 

 pp. 91 et seqq.~\. 



The nephrite of Southern Liguria has recently been the subject of 

 a paper by Dr. Kalkowsky [17]. The mineral occurs in association 

 with talc, serpentine, and calcite, the less-altered rock-types being 

 euphotide or other saussurite-bearing rock. The nephrite is always 

 found in the neighbourhood of faults or dislocations. He emphasizes 

 the fact that nephrite is to be regarded as a rock or as a mineral- 

 aggregate, rather than as a mineral, and he considers that it was 

 here formed under deep-seated conditions by dynamic metamorphism 

 of the serpentine-talc-carbonate rocks, assisted by movement and 

 intense pressure [17, p. 375]. 



On reviewing the evidence as to the genesis of different nephrites, 

 it appears that no one universal mode of origin for the mineral can 

 be asserted ; each occurrence must be studied on its own merits. 

 Jadeite having been shown to be a product of metamorphism of 

 alkaline rocks [12, p. 187], it is evident that nephrite, which nearly 

 always occurs in association with ultrabasic rocks or their alteration- 

 products, cannot often have been derived by uralitization of jadeite. 



