212 
MR. C. BARRINGTON BROWN AND PROFESSOR J. W. JUDD 
stone brought from the ruby-cave at Mogok by Mr. Barrington Brown, there occurs 
a colourless crystal of high lustre with curved faces, which was naturally taken, at 
first sight, for a diamond. A careful measurement of the angles by Mr. H. A. Miers, 
of the British Museum, however, suggested that the mineral must be zircon. Strange 
to say, however, when this specimen was sealed up in a vacuum-tube by Mr. Crookes, 
and submitted to an electric discharge, it gave a phosphorescence very similar to 
that of many diamonds, and very different from that of most zircons. But an 
undoubted zircon from washings at Burma, when sealed up and exposed to the 
electric discharge, exhibited the same remarkable phosphorescence. For the applica¬ 
tion of these important tests, and much other valuable aid in the study of these 
minerals, I am greatly indebted to Mr. W. Crookes, F. B.S. 
4. Garnets , which are so abundant in the gneiss rocks that are interfoliated with 
the limestones, occur also in the latter rocks themselves. Almandine, andradite, and 
more rarely grossular garnets occur, crystals over a pound in weight being some¬ 
times found. Like the accompanying minerals, the garnets are often found undergoing 
various stages of alteration; and in the gravels there are frequently found pseudo- 
morphs of garnet crystals, which crumble to pieces when handled. 
5. Apatite of a beautiful and unusual blue tint is found in some of the washings, 
mingled with the other gems. It forms well-defined crystals. 
6. Felspars of several species, both orthoclastic and plagioclastic, abound in the 
washings. The orthoclase often exhibits the Murchisonite parting, with the peculiar 
schiller due to reflection from air films characteristic of that variety. Not unfrequently 
the varieties with brilliant reflections from included scales (sunstone), and those with 
opalescence and chatoyance (moonstones), are found. In many cases the felspar- 
crystals, as they occur in the washings, are completely converted into kaolin, and 
sometimes they are, to a greater or less extent, changed into epidote. In one case, a 
large felspar-crystal was found in which alteration into epidote had gone on along the 
two principal planes of cleavage, the result being a mass which weathered, with 
surfaces that suggested organic structure. 
7. Quartz of different varieties is found in nearly all the ruby-earths. Milk-quartz, 
rose-quartz, and amethyst occur, but are rare, while citrine and smoky quartz are 
common. Many beautiful examples of parallel growths are seen, and, in the case of a 
fine example from a mine at Mogok, this parallel growth is accompanied by a spiral 
twisting of the principal axis of the crystal, resulting in forms like those of Trabecs- 
thal, which have been lately so admirably investigated by Tschermak.* Even the 
quartz has not escaped the alteration so universally exhibited by the minerals of 
these ruby-bearing rocks. We find the quartz-crystals to be, in nearly all cases, 
pitted all over with naturally etched figures ( Verwitterungs-Jiguren), often of a very 
interesting character. 
8. Micas .—Phlogopite is one of the most common constituents of the corundiferous 
* ‘ Denks. k.k, Akacl. Wissenscli., Wien Math.-Naturwissensch. Cl.,’ Bd. 61 (1S91), p. 365, 
