74 COKUNDUM, ITS OCCURRENCE AND DISTRIBUTION. 
ture of 530°. In this reaction the excess of ahimina separated out as 
corundum. When the temperature was raised to 400° only diaspore 
was produced, at 450° to 500° both corundum and diaspore were 
obtained, and at 580° to 535° only corundum. When the soda con- 
tains a small amount of aluminum and calcium carbonates small 
crystals of calcite are obtained with the corundum. 
By the action of alumina, with more or less potash, and barium 
fluoride heated to a very high temperature in an earthen crucible, 
Fremy « obtained in 1891 ruby corundum that w^as well crystallized, 
clear, and of a brilliant color, potassium bicarbonate having been 
used as a coloring matter. Corundum '^ has also been produced by the 
action of aluminum chloride on lime. 
Some of the more instructive artificial productions of corundum 
iire those which have been obtained from molten magmas whose 
chemical composition was approximately that of known rocks. This 
synthetic production of corundum has aided very materially in solv- 
ing the problems relating to the origin of corundmn in nature. 
Hautefeuille ^ has described the production of corundum by dis- 
solving alumina in nepheline, whence resulted a vitreous paste from 
which many hexagonal plates of corundum separated. 
Morozewicz '^ in his recent elaborate work on the Experimental 
Investigation of the Formation of the Minerals in an Igneous Magma 
describes the formation of corundum from many of the magmas 
that were supersaturated with alumina. The supersaturated alumina- 
silicate magmas have the general composition MeOmAloO;{/^SiO. 
(Me=K2, Nao, Ca, but not Fe or Mg; n=:2 — 13). These magmas 
in cooling, when magnesia and iron are not present, throw out all 
their excess of alumina (over m=l) in the form of corundum crys- 
tals. (See also p. 89.) 
In the crystallization of an anorthite-nepheline magma which did 
not contain any magnesia, the principal products were corundum, 
anorthite, and nepheline. 
Another interesting method of producing corundum is in the reduc- 
tion of certain of the rarer metallic oxides by the aid of powdered 
metallic aluminum, corundum being one of the products of thc^ 
reaction, which is dependent upon the strong affinity of the aluminum 
for oxygen. In this reaction the metallic oxides are mixed in a 
refractory crucible with finely powdered aluminum and barium 
peroxide, the latter containing an excess of oxygen and being readily 
" Synthase des Rubis (Paris), 1891. 
" Dana. Mineralogy, 1892, p. 213. 
'• Bull. Soc. frang. de mineral., vol. 13, p. 147 ; Am. Naturalist, Nov., 1890, p. 1076. 
" Tscliermaks mineral, und petrog. Mittlieil., vol. 18, 1898, pp. 1-90, 105-240 ; and 
review of same in Jour, (ieology, vol. 7, 1899, pp. 300-313. 
