^ 



150 



I. II. 



Si0 2 ... ... 50-49 ... ... 53-05 



A1 2 3 ... ... 25-27 ... ... 24-24 



Fe 2 3 ... ... 3-36 ... ... 3-37 



CaO ... ... 11-07 ... ... 12-17 



MgO ... ... 2-70 



Na,0 ... ... 4-93 ... ... 4-86 



K 2 ... ... 1-30 ... ... 1-35 



HoO 2-11 0-96 



101-23 100-00 



I. Bulk analysis of the saussurite. 



II. Chemical composition corresponding to the above mineralogical com- 



position. 



Microscopic examination showed that the substance contained chlorite, 

 actinolite and calcite in addition to zoisite, epidote and felspar. The difference 

 between the observed and calculated results may therefore be accounted for 

 by the presence of accessory constituents. The principal conclusions of the 

 author may be summed up as follows : 



(1) The so-called saussurite is not an independent mineral, but a 



mixture of plagioclase (more rarely orthoclase) with zoisite. 

 Actinolite, chlorite and other minerals occur as accessory 

 constituents. 



(2) The chemical composition of the saussurite mostly resembles that 



of the soda-lime felspars. It is, however, poorer in silica, 

 richer in lime, and possesses a higher specific gravity. 



(3) Saussurite is a product of the metamorphosis of the felspar 



through interchange of silica and alkalies with lime, iron and 

 water. 



(4) The epidotisation of the felspar is an alteration process which 



stands in the closest relation with the formation of saussurite 

 (zoisitisation), and differs only in the fact that more iron is 

 taken up. 



An important question, not considered by CATHREIN, arises directly out 

 of his work. Is the albite an original or secondary felspar ? The saussurite, 

 it must be remembered, is a constituent of gabbro. Now, so far as we know, 

 the original felspars of gabbro invariably belong to the labradorite-anorthite 

 series. It is, to say the least, in the highest degree improbable that albite 

 can arise on a large scale as a direct product of the consolidation of a basic 

 magma. This consideration alone points, therefore, to the conclusion that the 

 albite, like the zoisite with which it is associated, is a secondary product. 

 This conclusion is confirmed when we remember that the zoisite and albite, 

 taken together, have practically the composition of a basic felspar, and that 

 the formation of albite, as a secondary product, in connection with the 

 metamorphosis of labradorite, has been established by LOSSEN in the case of 



