480 Prof. T. G. Boniiey and Miss C. A. Raisin. 



SiO, 38-22 



A1,O, 13-83 



Fe,0, 7-81 



CaO 25-55 



MgO 373 



K S 7-07 



Na,0 2-46 



Loss at red heat 1'89 



100-56 



Microscopic examination, no less than chemical analysis, shows 

 that this specimen cannot be referred to nephrite, and consists almost 

 certainly of more than one mineral. But it is very difficult to ascer- 

 tain what these may be. The microscope does not give much help, 

 for it indicates an aggregate of ill-defined constituents, which some- 

 times recall the structures seeu in examining the material named 

 saussurite. The chemical analysis is remarkable for its richness in 

 lime and alkalies (especially potash) and comparatively low per- 

 centages of silica and alumina. The general character of the rock 

 suggests the possibility of jadeite being an important, if not the main 

 constituent. But, according to Krenner,* the normal analysis of this 

 mineral is Si0 2 = 50-23,A1 2 3 = 25-37,Na,O = 15'40, and, though the 

 actual analyses of specimens (doubtless being mixtures) have gener- 

 ally rather more silica, and less alumina and soda, with a little lime 

 and protoxide of iron, still they do not correspond with the present 

 one. Apart from the difficulty of the presence of so much potash, 

 we should find, if we supposed the alkalies to be contained in jadeite, 

 hardly any silica or alumina left to go with the lime and other prot- 

 oxide constituents. Saussnrite would account for some of the alkalies 

 and of the lime, but it has nearly the same silica percentage as jadeite, 

 and a rather higher one of alumina. Zoisite (proper) epidote, the scapo- 

 lite group, and elceolite present, in each case, important differences. 

 Certain of the constituents agree fairly well with one of the lime 

 garnets.f The rock in which this occurs is said to be homogeneous, 

 tough, with a rather waxy lustre, and a yellowish-white colour 

 hardness = 7, and sp. gr. = 3'33 3'64. It gave, on analysis, SiO 

 = 44 85 ; A1 2 3 = 10' 76 ; Fe 2 s = 3'20 ; CaO = 34'38 ; MgO = 

 5-24; loss by ignition, MO. Total, 99'53; and of this Dr. Hunt 

 takes, for the garnet, Si0 2 = 22'69; A1 2 S = 10' 76; Fe a O 3 = 3'20; 

 CaO = 21-07. Total, 57-72. Such a mineral as this, if present in 

 considerable quantity, would leave in the Karakoram rock a fair 

 amount of silica for the alkalies and remaining protoxide bases. A 



* ' Neues Jahrb. f. Min.,' 1883, ii, p. 173. 



t T. S. Hunt, 'Amer. Jour. Sci.,' vol. 27 (1859), p. 342. 



