174 



and down the boule and that the top of the boule is flatter than iu the 

 other type. Iu such boules there is also evident a tendency toward form- 

 ing a hexagonal prism with faces and angles roughly apparent. Where 

 the flattening occurs on the side of the boule, which is the usual case, it 

 does not form a perfect plane, being apparently interfered with — perhaps 

 by the surface tension of the semi-plastic mass. The longest horizontal 

 diameter of the boules (they are made with tlie stem of the pear acting 

 as a vertical support) is invariably parallel to the flattened face. On the 

 side of the boule opposite to the flattened face there is sometimes another 

 and smaller flattened face approximately parallel to the first. This, too, 

 shows evidence of (list<irti<iu of the lines representing the edges of the 

 strata of accretion. 



From what has been advanced in regard to these imperfectly devel- 

 oped basal faces I think tliat the term MiiluMlral as used to describe the 

 boule should be qualified. The boules are nearly anhedral, but not quite 

 so. The forces of crystalliziition succeeded in forming a single crystal in 

 spite of the adverse forces acting upon the boule, )>ut they wore unable to 

 face up the crystal except imperfectly, as has been described. 



I will now pass to my next topic and offer evidence of the hexagonal 

 character of the Ixtules. On exaiuining tlic llattened surfaces described 

 above, by means of a compound mlcroscoite with a magnification of several 

 hundred diameters, I found that by proper focusing I was able to trace 

 the outlines of minute crystals whicli formed a species of frost work upon 

 the surface of the boule. Thr'se crystals were all of similar orientation, 

 and their orientation was ne;irly that of the boule itself. When viewed 

 perpeudicuhuly to the flattened place on the boule the minute crystals had 

 hexagonal forms (Figs. I a and h). When viewed at right angles to the 

 basal plane of the boule rectangular figiu'es representing the edges of 

 hexagonal idatcs were seen (Figs. 11 a and lil. The evident hexagonal 

 form of these minute components of the crystal and their common ori- 

 entation would seem to prove th<! hexagonal character of the boule on a 

 crystallographic basis indeiM'udently of the optical evidence. 



I find also that by examining fractured surfaces of ruby boules with 

 similar niagnifi<-at!on (i. e., several hundred diameters) I can find sharp 

 hexagonal cavities out of which hexagonal plates have been torn by tin; 

 fracture as though there had been a species of molecular cleavage. This, 

 too, would seem to confirm from a crystallograi>hic basis the hexagonal 

 struc-ture of the boule. 



