ON THE RUBIES OF BURMA. AND ASSOCIATED MINERALS. 
211 
familiar gliding planes following the primitive rhombohedron have been developed by 
pressure and intensified by subsequent chemical change. 
The clear and brilliantly coloured rubies seldom, if ever, attain to great dimensions, 
either in the Burma limestones or in the alluvia ; but masses of red corundum are 
occasionally found weighing several pounds. [Occasionally specimens are found 
showing a perfect transition from the dull red crystalline corundum into the trans¬ 
parent and lustrous ruby. I am indebted to the Burma-Ruby-Mining Company for 
a beautiful illustration of this transition.—November 30, 1895.] 
2. Spinels .—In the beauty of their colour and lustre the spinels found in the 
Burma limestones are scarcely inferior to the corundums, but they are of course 
wanting in that play of colour which results from the possession of the property of 
pleochroism. They more frequently exhibit their proper crystalline form—the 
octahedron without modifications—than do the corundums ; but twinned forms 
appear to be rare. Various tints of red are the most common colours, specimens from 
the palest pink to the deepest crimson being found. The average specific gravity of 
these red spinels, determined on a number of carefully selected examples, was 3"52. 
With the red spinels, however, there occur more rarely various shades of blue, violet, 
brownish, and occasionally black (ceylanite). The faces usually exhibit etched 
figures, and, as we shall see in the sequel, alteration forms of the mineral are very 
abundant. The fracture is almost always conchoidal, and only rarely do we find 
traces of the parting (probably of secondary origin) parallel to the octahedral faces. 
The proportion of spinel to corundum, at different localities in Burma, appears to 
vary to a very marked extent. At Sagyin, spinels are very abundant, and rubies 
comparatively rare, while in the limestone of Mogok, the red corundum abounds and 
the spinels are in nothing like such great excess. In a mass of gems brought home 
from a twinlone at Mogok, by Mr. Barrington Brown, I found that the spinels 
weighed 54*39 grams, or 64 per cent, of the whole, and the corundums 30‘33 grams, 
or 36 per cent. All the spinels from this pit were various shades of red, with the 
exception of 0'39 gram of shades of blue spinel. Among the corundums, 25'87 grams 
were various shades of red, 1*20 grams were blue (sapphire), 2*57 were yellow (oriental 
topaz), and 0*69 purple (oriental amethyst). 
A prospecting pit, sunk by Mr. Barrington Brown at Bernardmyo, yielded, how¬ 
ever, very different results. The washing of about two cubic yards of earth yielded 
76*71 grams gems, in which I found 63*89 grams, or 83 per cent., of spinels, mostly 
red, and 12*82 grams, or 17 per cent., of corundum. The latter comprised 5*65 grams 
of colour and clearness, entitling them to be called “rubies,” 1*26 grams of sapphire, 
and 6*91 grams of red corundum. 
3. Zircon occurs but rarely in association with the corundums and spinels of Burma. 
Well-developed crystals are found in the washings, consisting of the combination of 
prism and pyramid (co P and P : 110, 111). These zircons are nearly colourless, have 
a remarkable lustre, and may easily be mistaken for diamonds. In a mass of lime- 
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