486 
THE GEOLOGIST. 
difference. Instead of a charcoal crucible, a crucible of alumina is 
used ; and instead of a charcoal cupel for the boric acid, a platinum 
one is preferred The colour of the rubies thus obtained is identical 
with that of the natural specimens. The ros}'-violet tint so much 
admired in the natural gem is present in the artificial one, where it is 
due to sesquioxide of chromium. 
3. Sapphire. — The sapphire, or blue corundum, is produced under 
the same circumstances as the ruby. It is also coloured with chromic 
oxide, the onl}^ difference between them consisting in the proportion 
of the colouring substance. Perhaps, also, there is a slight difference 
in the degree of oxidation undergone by the chromium in the case of 
sapphire production. But in such cases analysis can teach nothing, as 
the quantities of colouring matter in either case is so extremely small. 
In some cases, the authors of the memoirs alluded to above have 
obtained, at the same time, crystals of ruby and crystals of sapphire, 
the former of a red colour, the second of a magnificent blue tint 
identical with that of the oriental sapphire. 
4. Green corundum. — When the quantity of chromic oxide in these 
experiments is very considerable, the corundum obtained is of a brilliant 
green colour, similar to that of Ouwarovite, a mint ral to which we have 
already alluded in the Gkologist,* as containing 3o'5 per cent, of oxide 
of chrome (according to Dr. Lewy and others) but which, from M. 
Damour's analysis, appears to contain only 25 ]ier cent. This green 
corundum is always formed in that part of ti e crucible where the 
fluoride of aluminium and the fluoride of chromium are placed ; the 
latter becoming relatively more and more concentrated as the operation 
proceeds (on account of its being the least volatile of the two com- 
pounds), explains how it is that this green variety of corundum is 
produced in this case in preference to the ruby or sapphire varieties. f 
5. Zircone. — Is produced by the same process as corundum (except 
that fluoride of zirconium is employed in the place of fluoride of 
aluminum). The zircone, or oxide of zirconium, shows itself in the 
shape of minute crystals regularly grouped in arborizations not unlike 
those obtained sometimes with sal-ammoniac. The chemical properties 
of zircone thus obtained are the same as those of the natural speci- 
mens ; but nothing is stated concerning the mineralogical or crystallo- 
graphical characters. 
6. — Ihe authors proceed to state that they have also obtained, by the 
above method of experimentation, crystallized oxides of other metals, 
e. g. of uranium, titanium, and tin. Eut neither their crystalline forms 
nor their chemical composition have yet been investigated sufficiently to 
be spoken of with certainty. 
7. Cymophane or Chrysoheryl. — This mineral is an aluminate of 
glucina, i.e. a compound of alumina and glucina. It is much prized by 
jewellers, as it is capable of taking a fine polish, and produces a magni- 
ficent gem when well cut. The French jewellers call it Chrysolite 
orientale, whereby it is often mistaken for yellow corundum, which goes 
under the same denomination. The colour varies from yellow to greenish 
* The Geologist, No. I., p 66. 
t All the above -varieties of corundum are met with in nature. — T. L. P. 
