Carl Fred. Kolderup. [Nr. 8 



If the original rock has chiefly consisted of olivine. the meta- 

 morphism into serpentine must have tåken placc according to 

 the following formula: 



Mge Fe 3 Si 4 Oie -f 4 H 2 = 2 H 4 Mgj Si 2 0» + 2 Fe 



4 olivine 2 serpentine 



2 Fe must, I suppose, be regarded as -\- Fe 3 O4, what seems 

 to be in conformity with what is microscopically observed concer- 

 ning the separation of small grains of magnetito. 



We know that difference of opinions has reigned how far ser- 

 pentine is to be regarded as a mere weathering-product of olivin- 

 rock, or as a real crystalline schist. On this occassion I want 

 to draw the attention to the fact that the occurrences of serpentine 

 in question most frequently have their longitudinal direction parallel 

 to the prevailing direction of the strike and foliation of the adjacent 

 phyllites, and that most often a foliation-structure has developed 

 in the scrpentines It is also antigorite which is the predominant 

 serpentine-mineral. In his paper '"Studien ilber Eruptivgesteine", 

 Løwingson-Lessing in 1899 proved that the rock-forming minerals 

 have a molecular volumc which is either less or greater than the 

 sum-total of the cornposing oxydes. The first group which has 

 been designated as the -r- group of the minerals, belongs essenti- 

 ally to the crystalline schists. Antigorite is the most conspicuous 

 -f- mineral among the serpentine-minerals. The serpentines of the 

 Samnanger- area are thus scarcely to be regarded as mere weather- 

 ing-products of olivine-rocks, although such a weathering-process 

 is most likely to have tåken plaee at an early stage; they must 

 be looked upon as crystalline schists, which have been formed by 

 pressure-metamorphism, as is otherwise the case with the rocks in 

 the upper zcme of the earth's crust, where folding of the mountain- 

 chains have tåken place. 



Under the above supposition that olivine consists of 3 forsterite- 

 and 1 fajalite-molecules. and that the 2 Fe is to be regarded 

 as i Fe ;j Oi, the molecular volumes are as follows: 



3 forsterite = 131.7 2 serpentine = 218 



1 fayalite = 47.3 | magnetite = 22.4 



4 H, = 72.0 



251.0 240.4 



