352 Spodumene and its Alterations. 



in rare but perfect crystals. This succession of minerals in the 

 secondary vein is not as regular as might he inferred from the 

 foregoing description, in which it is intended to indicate only the 

 general tendency toward a definite arrangement. 



At Walnut Hill, in Huntington, the material of the main vein 

 is similar to that of the preceding locality. In the secondary 

 vein, the first deposit was found to be a very coarse albitic 

 granite, rich in black Tourmaline, in huge masses, Muscovite 

 and Garnet : then followed Cleavelaudite, white Quartz, and 

 Spodumene, in the well-known fine crystals, associated with 

 black and blue Tourmaline, Triphylite, Cyrtolite, Garnet, Apa- 

 tite, Muscovite, and greenish-white Beryl : and the central sheet 

 of smoky Quartz received the terminations of the Spodumene- 

 crystals, together with a little Beryl, Muscovite, and Cyrtolite. 



The Spodumene, and in part its associates, in these veins, have 

 been affected by two successive processes of alteration. The one, 

 which may be denominated Hydro -thermal, occurred, perhaps 

 before the folding of the strata, during subsidence to that depth 

 below the surface at which they are known to be subjected to the 

 long-continued action of alkaline solutions at a high tempera- 

 ture. The other, to which the term Meteoric may be ap- 

 plied, has been continued up to the recent period, with the strata 

 in their present position, by solutions derived from the rain- 

 water, soil, and the decomposed feldspars in the weathered super- 

 ficies of the main granite-vein. 



Hydro-thermal Alteration. 



The passage of heated solutions, rich in alkaline silicates, over 

 the crystals of Spodumene, resulted at first in the simple sub- 

 stitution of the alkalies and of water, in various but definite 

 proportions, for the protoxides in that mineral, by the modes of 

 replacement already fully explained. The larger masses were 

 in most cases only superficially altered, but in the smaller and 

 slender crystals the process of substitution became complete. 



The alteration first attacked the superficies of a crystal, was 

 hastened by penetration along any existing fissures, and generally 

 progressed most rapidly from the termination of a crystal along 

 the plane of orthodiagonal cleavage. In the brittle, easily fis- 



