Spodumene and its Alterations. 353 



sured, and porous quartz-matrix of the Chesterfield vein, the 

 crystals of Spodumene were thus attacked from all sides ; but in 

 the dense compact envelopment of the crystals of the Barrus 

 locality in Goshen, the attack proceeded only in the direction of 

 the longer axis of the prism along the orthodiagonal plane. 

 The formation of the hydrous minerals was then gradually in- 

 terrupted, and finally ceased, as new conditions of more rapid 

 alteration came into existence, perhaps partly by greater satura- 

 tion with alkaline and other salts, and partly by increase of 

 temperature. The facts seem strongly to indicate that these 

 conditions varied greatly and frequently, not only in time but 

 in different parts of the vein, and of the same crystal, within 

 even a few inches ! Sometimes as the one or the other of the 

 two main alkalies predominated in a percolating solution, altera- 

 tion-pseudomorphs were produced, — of Albite, by addition of 

 silica and substitution of soda for the more soluble lithium- 

 silicate — and of Muscovite, by substitution of potassa and sepa- 

 ration of an equivalent amount of silica in the form of free 

 Quartz. The more rapid character of these processes naturally 

 facilitated the production of displacement-pseudomorphs in Mus- 

 covite, Albite, and Quartz, by the complete removal and re- 

 combination of constituents. 



Meteokic Alteration. 



The subsequent process of alteration — or rather decomposition 

 — and one which has continued up to the present time, upon the 

 cores of Spodumene remaining unaltered by the preceding pro- 

 cess, has been effected by ordinary meteoric waters, at times 

 holding in solution the acids derived from the decomposition of 

 humus. By ordinary carbonated waters, there has been a 

 gradual removal of a part of the lithia and more soluble protox- 

 ides, almost universal, with the consequent effect upon the 

 physical characteristics of the mineral, shown by the loss of 

 weight, lustre, greenish color, and translucency. The channels for 

 the passage of these solutions have been the increased number 

 of fissures in the surrounding gangue, and in the altered crystals 

 themselves, as well as the capillary vacuity along the contact- 

 line between the core of each crystal and its alteration-crust. 



