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MR. C. BARRINGTON BROWN AND PROFESSOR J. W. JUDD 
seen to display a series of step-like ridges like those of a contoured model, or those 
exhibited by the well-known Babel quartz (see fig. 18, c.). # This character is admir¬ 
ably illustrated by the fine ruby (evidently from Burma) which has been presented by 
Mr. Buskin to the British Museum collection, under the name of the “ Edwardes 
Ruby.” It is evident that the hydration and conversion of the corundum into 
diaspore has not gone on with perfect uniformity, but has been controlled by the 
existence of planes of chemical weakness parallel to the faces of the primitive rhombo- 
hedron. 
In some cases, however, the eating into the corundum crystal by the formation of 
the hydrate (diaspore) appears to go on in a very capricious manner indeed; irregular 
depressions are formed extending quite into the interior of the crystal (see fig. 18, a 
and b), and thus it is gradually reduced to a shapeless mass. 
The most characteristic of all the methods of breaking up of the Burmese rubies by 
hydration and chemical action is that exhibited when the rhombohedral faces of the 
crystals are attacked along the twinning planes that become solution-planes. 
Fig. 19. 
In the specimen figured above (fig. 19), which is enlarged 5 diameters, a piece of the 
Mogok limestone, showing both cleavage and twinning planes, is seen having embedded 
* [It might, of course, be argued that the peculiar forms of these corundums aud spinels are due to 
iri’egularities in the growth of the crystals, as in the Babel quartz and certain varieties of fluor and 
many other minerals. But that, in the case of the corundums and spinels of Burma, the appearances 
presented are actually due to corrosion seems to be proved by the fact that in so many instances the 
products of alteration can be seen still surrounding the unaltered gems.-—October 7, 1895.] 
