210 
MR. C. BARRINGTON BROWN AND PROFESSOR J. W. JUDD 
ficial crystals the degree of development of the basal plane (OR) is usually much 
greater, and the crystals thus come to assume a tabular character. 
In order to obtain the specific gravity of the Burma rubies, a selection of clear 
finely coloured gems was made from the washings brought from Burma by 
Mr. Barrington Brown, and their density was determined by the pycnometer. 
The average density of the Burmese gem was found to be 4'03. De Bouenon found 
the average density of twenty rubies, of which the localit}^ is not stated, to be 3'08. 
Most of the associated red corundums of Burma have a considerably lower density, 
and in the case of one crystal, showing marked indications of chemical change, it was 
found to be as low as 3'74. 
The colours of the Burma corundums are very variable. Every shade from white 
through various shades of pink up to the deep crimson (pigeon’s-blood colour), which 
is so highly prized, may be found. The stones are not unfrequently parti-coloured, 
and variable in tint in different portions. Mr. Barrington Brown brought home a 
remarkable specimen, which was colourless at one end and graduated at the other end 
into the most beautiful and intense red. All the coloured varieties of corundum 
occur, but in much smaller quantities than the red ones ; blue of every depth of tint 
(sapphires), yellow' (oriental topaz), purple (oriental amethyst) are not rare ; but the 
green varieties (oriental emerald, oriental chrysolite, and oriental aquamarines) with 
the colourless ones (white sapphires) appear to be of very exceptional occurrence. 
The pleochroism of the Burma rubies of course varies with their colour, but there 
seem to be constant peculiarities in the pleochroism of gems of different districts 
which can be detected by the aid of the dichroiscope. Thus the sapphires of Burma, 
like those of Ceylon, show tints of blue and straw-colour with the dichroiscope, 
while the Siam sapphires give blue and a decided green colour. In the same way, 
while the fine rubies of Burma give crimson and aurora-reel tints for the ordinary 
and extraordinary ray respectively, the less finely coloured stones from Siam give 
crimson and a broumish-red tint for the two rays. 
The Burma rubies not unfrequently exhibit cavities, sometimes of considerable size, 
and often of very irregular form. These cavities sometimes contain a liquid and 
bubble (carbon dioxide), but in other cases appear to be filled with solid matter—a 
reddish-brown glass in some instances. Not unfrequently we find the rubies filled with 
acicular or platy inclusions arranged along the rhombohedral planes and intersecting 
one another at angles of 60°. These give rise to the beautiful phenomenon of 
asterism. In some cases, a well-marked zoned structure is exhibited by crystals, in 
which layers filled with inclusions, and giving a striking “ schiller,” alternate with 
clear bands without inclusions. A remarkable example of this kind is in the 
possession of Mr. Streeter. 
In the great majority of cases the Burma rubies exhibit a perfectly irregular or 
conchoidal fracture, like that of quartz. Chemical alteration sometimes leads to the 
formation of a secondary parting along the basal plane, while still more rarely the 
