228 ON THE RUBIES OF BURMA AND ASSOCIATED MINERALS. 
largely replaced by a green or brown hornblende, the latter resembling 
basaltine in its scheme of pleochroism. At the upper part is seen an 
interesting intergrowth of pyroxene with plagioclase felspar and quartz 
resembling the “ centric structure ” of Becke. X (These pyroxenites 
and amphibolites alternate with limestones, and frequently graduate 
insensibly into the calciphyres.) 
Fig. 8. Tourmaline-felspar-quartz rock of Nyoungouk, which yields the rubellite of 
Burma, the tourmaline which is often beautifully zoned, is an indicolite. 
The felspar is plagioclastic and sometimes partially changed to scapolite, 
and the quartz is small in quantity. 
Fig. 9. Lapis-lazuli rock —consisting of white diopside, scapolite, and two blue con¬ 
stituents, one deeply tinted, the other pale-tinted (haiiyn and lazurite (?)), 
both perfectly isotropic. In different examples of this rock, the pro¬ 
portions of the white and blue minerals to one another vary greatly. 
The rock was not found in situ, but in blocks of considerable size in 
ruby workings at Thabanpin. X ~ 3 ~. 
The last three figures illustrate the general nature of the Mogok limestone, and of 
the alterations which take place in the spinels and rubies enclosed in it. 
Fig. 10. Section of limestone from ruby-cave, Mogok—a crystal of corundum is seen 
lying in this limestone, partially converted into diaspore and various 
secondary silicates. A bent crystal of the beautiful green chrome-mica 
(fuchsite) appears in the lower part of the mass and a granule of pyrrho- 
tite at the right. X - 3 ~. 
Fig. 11. Spinel and ruby in the midst of the limestone. Ruby-cave, Mogok, 
11a, shows a crystal of spinel much eaten into and undergoing- 
peripheral alteration, shown by change of colour. Masses of secondary 
silicates, pseudomorplious after spinel, and scales of graphite are also 
seen. X 11 b, from another part of the same slide, shows two 
granules of corundum (ruby) broken up and enveloped in diaspore, the 
whole being surrounded by a zone of mixed silicates. These are 
evidently examples of ruby undergoing change in the midst of the lime¬ 
stone rock. Xx- 
Fig. 12. Large ruby in the midst of the limestone of Mogok, partially changed into 
various silicates. Smaller crystals, two intact, and two partially altered, 
are seen near it. X “ 3 °. 
J. W. J. 
