ON THE RUBIES OF BURMA AND ASSOCIATED MINERALS. 
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limestones of Burma ; and in the ruby-earths hexagonal plates of mica with a 
diameter of from 20 to 30 centims. are frequently found. These phlogopites are 
some clear and almost colourless, but more usually show tints from smoke-brown to 
black. The angle between the optic axes of these phlogopites is shown by the 
interference figures to be small, never exceeding 20 or 30 degrees, and is often much 
less. In the ruby-earth muscovite, probably an alteration product from corundum, 
orthoclase and other minerals are frequently found. 
Fuchsite, or the beautiful green chrome-mica, certainly occurs in some of the 
samples of ruby-earth from Burma, and is also sometimes seen in the limestone 
containing rubies from Mogok (see Plate 6, fig. 10). 
9. Amphiboles are common in the ruby-earths and the limestone, and include several 
varieties of both green and brown hornblende with a variety near to arfvedsonite. 
10. Pyroxenes are particularly common, and include a nearly colourless sahlite, 
green diopside, and a green soda-pyroxene (aegerine), with a jade-like variety among 
the augites, and both bronzite and hypersthene among the enstatites; wollastonite is 
by no means rare in some of the limestones and associated rocks. 
11. Fibrolite (sillimanite) is also a constituent of the limestones. 
12. Scapolite is found in the limestone, but has not been detected in the ruby- 
earths ; it has probably disappeared through alteration processes, giving rise to the 
formation of calcite. 
13. Besides Muscovite and Gilbertite, other silicates found in these limestones, 
which probably represent decomposition products, are Margarite, and several other 
clintonites, and various chlorites and vermiculites. 
14. Kaolinite (nacrite ) is very abundant, probably derived from the felspars; and, 
indeed, this and similar hydrated silicates of aluminium appear to make up the bulk 
of the ruby-earths. 
15. Lapis-lazuli. —Among the interesting minerals brought from the ruby-earths 
of Burma, are great blocks of lapis-lazuli. These are of two varieties. In one, the 
quantity of blue mineral is so great that the rock-masses have a deep indigo tint, 
the quantity of white minerals being, as seen in thin sections under the microscope, 
comparatively small. In the other variety we have a white mass speckled with 
blue. Microscopic study of these rocks shows that we have several isotropic, blue 
minerals present (lazurite, hauyne, sodalite) and various nearly colourless minerals, 
including wliite-diopside, wollastonite, scapolite, epidote, and calcite. 
16. Graphite, often well crystallized, occurs in plates up to 8 or 10 centims. in 
diameter in the ruby-earths. It is also found to be present in almost all the 
limestones. 
17. Pyrrhotite, like graphite, is among the most widely distributed of the minerals 
in the limestones. It appears, like graphite, to be a constant associate of the rubies 
and spinels. 
In addition to these undoubted constituents of the Burma limestones, there are 
