116 Day and Allen — Isomorphism and Thermal 



Albite. — From the experiments upon natural albite and 

 orthoclase, which have been described, and after observing the 

 effect of the increasing viscosity as we approached the albite 

 end of the artificial plagioclase series, we had no expectation 

 of finding a melting point for either in the ordinary sense. 

 .Nor did we in fact succeed in locating a point of any real 

 significance in this connection. The various trials which were 

 made were simply calculated to throw all the light possible 

 upon the character of the change from (crystalline) solid to 

 liquid in such extremely viscous substances. The return 

 change or recrystallization of such substances from the melt 

 (solidifying point) without the introduction of modifying con- 

 ditions has never been accomplished. The time required to do 

 it is certainly very great, probably much greater than the 

 demonstration is worth at the present stage of experimentation 

 in this field. 



Crystalline albite has been produced under exceptional con- 

 ditions several times — by Hautefeuille,* by heating a very 

 alkaline alumino-silicate with sodium tungstate for 30 days at 

 900°-1000°; by Fried el and Sarasin,f using an atmosphere of 

 water-vapor under high pressure and a moderately high tem- 

 perature (an aqueo-igneous fusion); by J. Lenarci6,J at ordinary 

 pressure and high temperature by crystallization out of a mix- 

 ture of melted albite and magnetite (1 part magnetite, 2 parts 

 albite by weight), and by others. It may be noted in passing 

 that, entirely apart from the solution relations, the last 

 mentioned process reduces the viscosity to an entirely differ- 

 ent order of magnitude from that of pure albite ; magnetite 

 melts to form a thin liquid almost of the consistency of water 

 and even in 1:10 solution with albite forms a fairly mobile 

 liquid. We endeavored to repeat portions of the work of 

 Hautefeuille and Lenarcic, but were obliged to postpone a 

 systematic inquiry into the conditions of crystallization which 

 involved the addition of other components or extraordinary 

 pressures, until our plant could be somewhat extended. 



Hautefeuille describes his successful preparation as a " solu- 

 tion " of the alkaline alumino-silicate in sodium tungstate out 

 of which the albite slowly crystallizes after long heating, but 

 he remarks that the crystallization does not take place if the 

 mixture is heated sufficiently to melt the components of the 

 charge into a homogeneous glass. In that case he obtained 

 only a vitreous white enamel. The case does not appear, 

 therefore, to be one of simple solution, out of which the same 



* Hautefeuille, Annales de l'Ecole Normale Superieure, 2d series, ix, p. 363, 

 1880. 



f Friedel and Sarasin. Bull. Min., clviii, 1879; lxxi, 1881. 

 X J. Lenarcig, Centralblatt f. Min., xxiii, 705, 1903. 



