of the Brazilian Topaz. 7 
nucleus and the external tessele. In one specimen, a faint 
phosphorescent glow appeared and vanished at intervals in the 
nucleus, while the light shone in the outer border with a bright 
and permanent lustre. 
IV. On Substances found in the Brazilian Topaz. 
In a very great number of Brazilian Topazes there is a white 
pulverulent substance, which must have been formed at the 
same time with the mineral, as the most powerful Microscopes 
cannot detect any aperture or crevice through which it could 
have been admitted. Upon breaking up the specimens where it 
occurred, and examining the surfaces of the laminew between 
which it had lain, I found that they had been acted upon by 
the substances, as they exhibited that superficial disintegration 
which is produced by the action of a solvent, and which is 
identically the same with what is found on many of the summit 
planes of the crystal, as shewn in Fig. 15. This circumstance 
proves in the clearest manner the contemporaneous formation of 
the white powder. 
M. Berzelius, to whom I had transmitted some specimens 
of this substance had the goodness to analyse it for me, and 
found it to be a sort of Marle consisting of silex, alumina, lime, 
and water. ‘This substance, he remarks, if it were crystallized, 
would belong to Cronstedt’s family of the Zeolites.” From the 
frequency with which this matter occurs in the Brazilian Topaz, 
and the imperfect character of the crystallization which accom- 
panies it, I cannot help thinking, that it is nothing more than 
the uncrystallized ingredients, and that lime is one of the con- 
stituents of the mineral*. 
a NUON IME A A ee 
* When the crystal is placed upon a hot iron, the white portions are more phospho- 
rescent than the other parts. 
