ON THE RUBIES OF BURMA AND ASSOCIATED MINERALS 
215 
variety of corundum of Asia Minor also occurs in limestone. The last-mentioned 
author has proved that the following minerals enter into the constitution of the emery 
itself—corundum, magnetite, tourmaline, cliloritoid, muscovite, margarite, and 
calcite—the last three being probably products of the alteration of the corundum 
itself. The list of minerals found in the corundum-bearing limestone, according to 
these two authors, includes diaspore, gibbsite, (hydrargillite), spinels (including 
gahnite or zinc spinel), muscovite, phlogopite, biotite, vesuvian, margarite, ehloritoid, 
and other clintonites, rutile, ilmenite, magnetite, hematite, staurolite, kyanite, 
pholerite, kaolinite, and tourmaline. 
With respect to the origin of the remarkable limestone in which the Burmese gems 
occur, I have been unable to find the slightest evidence that it has been formed by 
the alteration and recrystallization of an organic deposit; on the contrary, all the 
facts point to a totally different conclusion. 
The limestones of Burma are, as we have seen, most closely associated and 
intimately interfoliated with granitic and gneissic rocks, and especially with the 
unstable pyroxene and scapolite-bearing gneisses. Between these pyroxene-gneisses 
and the limestone we find every intermediate type of rock. Gneisses in which calcite 
is an important constituent (see fig. 17, p. 203) pass quite insensibly into rocks in 
which the same varieties of pyroxenes, amphiboles, and mica occur, but in which, by 
the increase of calcite, the rock becomes a true “ calciphyre,” like that of Tiree. 
Now all modern researches point to the conclusion that the pyroxene- and other 
gneisses resembling those of Burma were of igneous origin, and the limestones have 
certainly not the appearance of having become associated with the gneisses by the 
intrusion of the latter among them. On the contrary, when we come to study the 
metamorphism of the minerals in these gneisses, calcite is found to be constantly one 
of the final products of the changes which have gone on in the rocks. The abundant 
lime-soda felspars (labradorites) of the pyroxene-gneisses have been everywhere 
converted into scapolites (dipyre, &c.), the change having being brought about (as in 
the case of the analogous rock of Bamle, which I have investigated) by the action of 
hydrochloric acid under pressure. For this change Lacroix has proposed to use the 
term “ Werneritization.” But the scapolite is itself a very unstable mineral, and 
calcite is the constant product of its decomposition. It appears to me probable, 
therefore, that the calcite so frequent in these highly crystalline rocks, whether 
occurring as disseminated crystals through the gneiss or as great interfoliated masses, 
is really neither altered organic limestones nor of ordinary chemical (tufaceous) 
origin, but have resulted from the metamorphism of the lime-bearing felspars. 
[If this be the case, it is, of course, necessary to suppose that the calcium carbonate 
has been often transported to new localities in solution, while the basic aluminium 
and other silicates have in some cases been broken up, so as to give rise to the 
formation of corundum, spinel, and the various other minerals occurring in the lime¬ 
stone or in the rocks so closely associated with it.—October 7th, 1895.] 
