ON THE RUBIER OF BURMA AND ASSOCIATED MINERALS. 
20 L 
alteration of titanoferrite. It seems probable that in this rock we have examples of 
both kinds of paramorphism between ilmenite and sphene. The original coloured 
sphene is seen passing through a white opaque compound into titanoferrite ; and on 
the other hand a colourless sphene occurs which is probably of secondary origin and 
results from an alteration of the titanoferrite which originally formed a constituent 
of the rock. 
The other accessory constituents of these interesting pyroxene gneisses are apatite, 
which is found enclosed in all the other minerals of the rock, zircon, which is abundant, 
and occasionally corundum. The existence of this mineral in these peculiar basic 
gneisses is a very interesting and, as we shall hereafter show, a very significant fact. 
Some of the chief types of these pyroxene gneisses are illustrated in figs. 15, 16, 
and 17, and in Plate 6, fig. 1. 
Rocks of similar mineralogical constitution to these coarse pyroxene-gneisses, but 
of finer texture and assuming a more or less perfect granulitic habit, appear to be 
by no means rare in Burma. They exhibit a great diversity in the characters of their 
constituent minerals, but nearly all consist of a lime- or lime-soda-felspar (more or 
less altered to scapolite and sometimes to calcite and quartz) and a pyroxene which 
may be some form either of enstatite or augite, or may be partially or wholly con¬ 
verted into a hornblende or a biotite. These rocks may be designated pyroxene- 
granulites and pyroxene-scapolite granulites, and I will proceed to describe some of 
their most interesting varieties. # 
On the ridge below Toungnee a rock was found in situ, which proves on micros¬ 
copic study to be a sahlite-scapolite-granulite (see Plate 6, fig. 3). In this rock a 
white augite (sahlite) is very abundant and constitutes not less than one half of the 
mass. The mineral seen in thin sections shows no trace of colour or pleochroism, it 
has the usual augite cleavages, but no trace of schiller planes, and its extinction-angle 
is low—apparently not exceeding 40°. With the augite a few grains of an enstatite 
(bronzite) also occur. The remainder of the rock is almost entirely made up of a 
scapolite often exhibiting traces of the commencement of decomposition. There is 
no distinct felspar found in the rock, but the scapolite not unfrequently shows, by the 
relics of a lamellar structure in it, that it has been produced by the alteration of a 
plagioclase. Zircons are found enclosed in all the other minerals, and a few garnets 
and crystals of sphene with corundum (?) are among the accessory minerals of this 
very interesting rock. 
A rock closely related to the last is found at Letnytaung mountain. It is an 
augite-scapolite-granulite (see Plate 6, fig. 2) and consists of the following minerals :— 
A dark-coloured augite, exhibiting in thin sections the purplish tints of the varieties 
of this mineral containing titanium, but with scarcely a trace of pleochroism, consti¬ 
tutes more than one-third of the rock ; the remainder of the rock is made up of 
* The interesting rock recently described by Mr. T. H. Holland as “ charnockite,” or hypersthene 
granite, is a massive rock of similar composition, but rich in orthoclase. 
MDCCCXCVI.-A. 2 D 
