OX THE RUBIES OF BURMA AND ASSOCIATED MINERALS. 
223 
in it a fine ruby of excellent colour. The rhombohedral faces of the crystal are found 
to exhibit the characteristic step-like surfaces, and upon these white patches of 
diaspore can still be seen. This mass of limestone exhibits several pseudomorphs after 
smaller rubies, and some grains of graphite and pyrrhotite, all enclosed in the calcite. 
[There is a remarkable analogy between the way in which the rubies of Burma 
break up along- their rhombohedral planes, during hydration, and the disintegration of 
the diamond during its oxidation (combustion). Mr. J. Joly, F.B.S., in his account 
of experiments made to determine the thermal expansion of the diamond (‘Nature,’ 
March 22, 1894) writes as follows :— 
“At a temperature of 850°, and indeed below this, observations were stopped by 
the ‘ efflorescence ’ upon the surface of the diamond of flaky particles which wriggled 
and twisted in a peculiar manner, finally disappearing. Once started, the ‘ combustion ’ 
continued till the temperature of the oven was lowered to 712°. Cooling the oven, I 
subsequently photographed one face of the diamond. The picture obtained shows the 
face with a lamellar appearance, which was produced entirely by the heating, as at 
starting the faces were smoothly curved. Such an appearance is occasionally observed 
upon specimens of diamond. This photograph, as well as the curve of expansion, 
were shown at the soiree of the Boyal Society in June, 1892.’’ 
I am greatly indebted to Mr. Joly for copies of this very interesting photograph, 
and for permission to insert a reproduction of it (fig. 20) in illustration of this paper.] 
—December 8, 1895. 
But there is yet another method of the breaking up of corundum and spinel 
crystals, which is of the greatest interest to crystallographers and mineralogists. 
