230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
As regards the remaining transparent gem stones, which fall into 
a group by reason of the fact that they contain silica as an essential 
component, their artificial production is of little importance. They 
can not be produced by the same process as corundum, owing to the 
fact, already alluded to, that under such conditions both pure silica 
and compound silicates yield an amorphous product, which has not 
the optical properties of the natural stone. One is constrained, for 
the artificial production of the crystalline material, to fall back upon 
methods similar to those employed in the earlier attempts to obtain 
ruby—obtaining the requisite composition by chemical reaction and 
maintaining the mass at a temperature just above its fusion point for 
a sufficient time to allow the silicate to crystallize out. 
Topaz, garnets, and zircon have been produced in this way experi- 
mentally as a matter of scientific interest, but the small stones pro- 
duced have no commercial value, and to describe their production 
in detail would only weary you to no purpose. The majority of these 
stones are of such common occurrence in nature, and consequently of 
such little value, that their artificial production in this manner is not 
a commercial proposition. 
An exception, however, must be made in the case of emerald, 
which ranks next in value to corundum, and many attempts have 
been made to produce it artificially. Reconstructed emeralds have 
been made by the Verneuil process, but these are, of course, amor- 
phous, and do not possess the double refraction and other properties 
consequent upon the crystalline structure of the natural stone. The 
problem of producing this stone artificially has not as yet been 
solved in fact. - 1 am quite aware in saying this that recent news- 
paper reports lead one to believe otherwise, but, as in the case of the 
diamond, such reports indicate either remarkable foresight on the 
part of the writers or show that their imagination is developed at the 
expense of their powers of accurate observation. 
There remain now to be considered those precious stones which are 
opaque, and owe their beauty entirely to color and structure. 
Turquoise is a stone formed under conditions which are easy to 
reproduce, and its artificial production was successfully accomplished, 
many years ago, by precipitating hydrated phosphate of aluminium 
with the requisite proportion of copper phosphate to give it the color 
and subjecting the precipitate whilst still damp to hydraulic pressure 
for a considerable time. Prepared in this way the artificial turquoise 
is so nearly identical with the natural that its identification is a 
matter of considerable difficulty. There is, however, generally, a 
slight difference in the specific gravity, hardness, and index of refrac- 
tion (when this can be measured), which will serve to distinguish it 
on careful examination. The only point in which there is any 
decided difference between the two is the behavior on heating, but 
