ON THE RUBIES OE BURMA AND ASSOCIATED MINERALS. 
225 
acted upon by solvents under pressure. The very interesting specimens from Sagyin, 
recently sent me by Mr. Holland, seem to prove that, in certain cases, the corrosion 
of the spinel crystals must have taken place before their enclosure in the limestone. 
The fine spinels, nearly an inch in diameter, are found with their surfaces showing 
the incipient alteration to which I have referred. In these cases, it would seem that 
the growth of the spinel crystals and their partial alteration by solvent action going 
on irregularly over their surfaces, must both have been accomplished before the 
deposition of the calcite in which they are now found to be completely embedded. Tn 
the case of the Mogok limestones, however, the fact that the unaltered rubies are seen 
lying in the midst of a mass of their alteration products, the w^hole being enclosed in 
the limestone, seems to prove conclusively that the changes took place after the 
formation of the latter rock.—October 7, 1895]. 
VIII. —Summary or Results. 
The chief scientific results to which we have been conducted by these studies, are 
as follows :— 
1. The famous rubies and spinels of Burma have now been found in situ in a highly 
crystalline limestone, containing various silicates and oxides, with pyrrhotite (magnetic 
pyrites) and graphite. 
2. The equally famous rubellite (red tourmaline), so highly prized by the Chinese, 
though found in the same district, does not occur in actual association with the 
corundum and spinel in the limestones, but is found in certain acid rocks (aplites) 
associated with the gneisses and schists. 
3. The limestone containing rubies and spinels is very intimately associated with 
certain highly basic foliated rocks pyroxene - gneisses and granulites, with 
pyroxenites and amphibolites. 
4. Unlike most crystalline limestones which have yielded corundum and spinel, 
the Mogok rock does not appear to contain silicates combined with fluorine and 
boron. 
5. The source of the crystallized aluminium oxide (corundum), the aluminate of 
magnesium (spinel), and the calcite in which these minerals are embedded, appears to 
be the basic lime-felspar (anorthite) and associated minerals of the pyroxene-gneisses. 
The anorthite is often converted into scapolite, from which calcite and various 
hydrated aluminous silicates have been formed by further alteration. 
6. The hydrous aluminous silicates have been shown, under certain conditions, to 
break up and give rise to silica (opal) and hydrated aluminium oxide (diaspore, 
gibbsite, bauxite, &c.). 
7. The hydrated aluminium oxide, under other conditions of temperature and 
pressure, becomes dehydrated and may crystallize as corundum. 
8. While the crystallized aluminium oxide at the earth’s surface is one of the 
MDCCCXCVI.—A. 2 G 
