Igneous Rocks of Sviatoy Noss in Transbaikalia. J3 
3 ; Å N:o 1) 
The mean composition of the plagioclase in the rock, 
as calculated from the chemical analysis, is AbyzAn,. The 
microscopic examination gives a little higher percentages of 
the anorthite, namely from 9 to 14 percent. 
The average diameter of the ground-mass grains is about 
3 1 mm. The plagioclase as well as the pörast feldspar is fairly 
unaltered. 
The andradite usually occurs in the form of 
euhedral crystals of the dodecahedron form that are often 
surrounded by pyroxene. When enclosed in the garnet, as 
often is the case, the pyroxene is idiomorphic towards the 
= former. The amount of the garnet varies from 0 to about 
så 
- 
DN 
- 
: 
2 
F 
15 or 20 percént being largest in the specimens of type I. 
: Under the microscope the andradite shows a brown colour 
and is optically perfectly isotropic. This mineral is unaltered 
and contains many inclusions. Among these are found nearly 
all the other minerals of the rock except the feldspars. Pyro- 
xene occasionally occurs as rather large crystals. Apatite 
is much commoner as inclusions in the garnet than elsewhere. 
— Magnetite, epidote and orthite have all been met with. But 
especially are the crystals of titanite remarkably frequent 
in the garnet. Most of them are anhedral, in a striking 
contrast to those crystals embedded in the feldspar mass. 
These enclosed crystals of titanite will be subject to farther 
comment in the subsequent discussion of the composition 
«> of the garnet. | 
The andradite in the sviatonossite has undoubtedly ori- 
ginated by crystallization from the magma. In its composi- 
tion it shows, however, strong resemblance to the garnet of 
the skarn-rocks, found at the contacts between limestones 
and igneous rocks. Such andradite-skarn is also very com- 
mon on the peninsula of Sviatoy Noss as enclosed fragments 
in the igneous rocks. To compare the composition of the 
andradite from the sviatonossite with that of the skarn- 
andradite I analyzed the andradite from a fragment of skarn 
enclosed in the aplitic granite on the southeastern shore of 
Sviatoy Noss. The skarn-rock consists chiely of andradite 
with greenish pyroxene (diopside-hedenbergite), and smaller 
