174 



and duwu llio boule and that the top of the b(jule is flatter than in the 

 other type. In sucli boides tliere 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 nf llie senii-plastii- mass. The longest horizontal 

 diameter of the boules (tliey are niade with tlie stem of the pear acting 

 as a vertical support) is invariably iiarallel 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 distortion of the lines representing the edges of the 

 str;ita of accretion. 



Fronj what has been advanced in regard to these Imperfectly devel- 

 oped basal faces I think that the term anhedral as used to describe the 

 boule should be (jualirted. Tlie boules are nearly aiihedral, but not quite 

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

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

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



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

 character of the boules. On examining the flattened surfaces described 

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

 hn.ndred diameters, I found that by proper focusing I was able to trace 

 the outlines of minute crystals \^'hich formed a species of frost work upon 

 the surface of tlie l)oule. Those crystals were all of similar orientation, 

 and their orientation was nearly that of the boule itself. When viewed 

 peri)en(licularly to the flattened i)lace on the boule the minute crystals had 

 liexagoiial foi-nis (Figs. I a and b). When viewed at right angles to the 

 basal plane of tli(> lioiil(> i-ectangular figures representing the etlges of 

 he.xagonal plates wt're seen (^Figs. IT a and h). The evident hexagonal 

 form of these minute coniponeiits of the crystal and their eonunon ori- 

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

 crystallographic basis indeiK-ndently of tin* ojjtical evidence. 



I liml also that b.v examining tract ui'ed surfaces of ruby boules wilb 

 similar magnificat mui M. e., srvei'al linndred dia.meters) T can tind sharp 

 hexagonal cavities (int of wldcb liex.igonal plates have been torn by the 

 fracture as though there bad been a sjjecies of molecular cleavage. This, 

 too. w(Mild siH'ni to continii from a crystallograi.'hie basis the liexagonal 

 structui-e of the boule. 



