FER PYroFCES 2 SR 
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A N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. JA 
of the great ancient orogenetic period, before the main part 
of the chemical metamorphism had been performed. 
Diopside-pegmatite. 
On the western shore of Sviatoy Noss, pegmatites as well 
as other rocks were observed mainly as boulders of the shore- 
drift. Here was observed a special type of pegmatite which 
was later found to be largely distributed and characteristic of 
the Transbaikalian crystalline region, being found in all the 
tracts where limestones have an extensive occurrence. This 
pegmatite is characterized by the occurrence of diopside as 
the main mafic mineral. In the following it will therefore 
be designated as diopside-pegmatite. Another very 
invariable and often abundant constituent is titanite. When 
first observed as blocks among those of the sviatonossite, 
this pegmatite was considered as belonging to the latter rock, 
but later observation proved this supposition erroneous: 
the diopside-pegmatite is really confined to the limestone 
and to the vicinity of the limestone masses. It occurs in all 
parts of the peninsula, but it does not form very large masses. 
Nor are all pegmatites intruded in limestone areas diopside- 
bearing: the common pegmatites are much commoner also 
in the limestones. 
The mineralogical composition of these pegmatites was 
found to be remarkably constant, though there is much 
variation in the quantitative proportions between the differ- 
ent minerals. Often plagioclase is the most abundant 
constituent. Studied microscopically, the plagioclase was 
found to have the composition of oligoclase, about Abgp. 
This mineral then forms the largest individuals, and m i- 
crocline is present as a fine-grained mortar between the 
plagioclase crystals. The latter also contain spot-like inclu- 
sions of microcline as a kind of antiperthitic intergrowth. 
In other cases the microcline is the dominant feldspar, form- 
ing the largest individuals. It is of a gray colour. Quartz 
is usually only present in small amounts. The diopside 
is greenish gray or nearly colourless, often having the pro- 
