and its Spherulitic Crystallization. Ill 



this particular form. Nor does the writer wish to atiirm as a 

 positive rule that in all minerals the attractioti causing growth 

 is less towards a pronounced face of cleavage than in other 

 directions. It does, however, appear to be a rather general 

 one. 



In addition to the elongation of tlie fibers in spherulites 

 there is also the branching to be taken into account. The 

 more rapid growth of the corners and edges of crystals, due 

 to their commanding a larger portion of the space which is 

 supplying the crystallizing material and tlais producing branch- 

 ing and skeleton growths, was brought to attention by Leh- 

 manu" and further elaborated by Rosenbuschf and needs no 

 further discussion here. In the treatment of the subject by 

 these authors, however, it is tacitly assumed that the molec- 

 ular attraction towards all faces of the growing crystal is the 

 same, or at least there is not mentioned anything to the con- 

 trary, and the view previously expressed by the writer, that 

 this may be different on different faces, brings into play another 

 factor. 



That the molten glass had attained a considerable degree of 

 viscosity before crystallization began is clearly indicated by 

 the spherulites seen in figs. B and C of the plate, since it was 

 great enough to support these denser bodies and prevent them 

 from sinking to the bottom. 



That the formation of the spherulites was a comparatively 

 rapid process, after crystallization once started, is plainly shown 

 by their occurrence in the manner figured in A of the plate. 

 They were not present, of course, in the molten glass in the 

 furnace before breakage occurred, and their appearance here 

 in flow lines proves thej' had formed before flowage motion of 

 the glass had ceased. However long a time viscous flowage 

 may continue in larger masses of Java, in this small body of 

 glass it must have had a relatively short period. 



From the foregoing discussion it appears that the produc- 

 tion of spherulites in an anhydrous molten glass depends upon 

 crystallization starting from a center and proceeding out- 

 wardly in all directions at a time when the molten solution had 

 attained such a degree of viscosity as to control the crystal 

 habit and also upon the composition being such as to produce 

 minerals which naturally grow in columnar forms. The tixne 

 interval between this point and that where the fall of tem- 

 perature increases the viscosity to such a degree as to prevent 

 further molecular movement evidently controls the size of 

 the spherulites. In the case of the huge spherulites described 

 by Cross:}: from Colorado this time interval must have been 

 relatively long. 



* Uebei- das Wachsthum der Krystalle, Zeitschr. f. Krysl., i, 462, 1877. 

 f Phys. der Min., 1885, p. 26, 4th ed., vol. 1, 361, 1904. ^Loc. cit. 



