ån 4 an Mkr MAT 
AA N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 31 
Considering the actual, or modal, composition, the above- 
named distinctive characters in the chemical composition 
show themselves in the following mineralogical features: In 
- the monzonites the plagioclase contains considerable amounts 
of anorthite, and the mafic minerals are diopsidic pyroxene, 
hornblende and sometimes biotite and olivine; in the sviato- 
nossites the plagioclase is highly sodic and the mafic minerals 
are pyroxene and andradite, the latter mineral corresponding 
to the normative wollastonite and hematite (in the norm 
appearing as magnetite), according to the following equation: 
3 CaSiO, + Fe,0, = CasFe,SizO,3. 
As the actual garnet also contains considerable amounts 
of alumina which enters into the grossularite-molecule, 
Caz Al, Siz0,., this alumina being reckoned as forming anor- 
thite in the norm, the modal anorthite is still less in quantity 
than the normative, and the plagioclase is in fact often 
nearly albitic. Thus the rock assumes a somewhat alkaline 
character, and some small amounts of aegirite molecules are 
formed entering the pyroxene. 
From the foregoing statements it is apparent that the 
rocks in consideration cannot be classed with the monzonites, 
if this group shall have the limits once defined by Brögger.. 
If the sviatonossites are compared with true syenites of 
the calcialkalic branch, the resemblance is found to be 
closer as regards the percentages of (Mg, Fe)O and of alkalies, 
"but in these rocks there is no such excessive amount of 
lime that could form andradite. In most cases the ferrous 
and magnesium oxides are in excess over the femic lime, 
and hornblende is usually present as a mafic mineral. More 
rarely the ferromagnesium oxides are nearly equal to the 
femic lime and then we have pyroxene-syenites containing 
diopsidic pyroxene. Such is the akerite from the Christiania 
- Region (analysis V). As the pyroxene also contains some 
alumina, in the norm calculated as being present in the 
anorthite, the actual plagioclase in the akerite is highly 
sodic. The mineral and chemical composition of the akerite 
were accordingly very similar to that of the sviatonossite 
6 
