Notes on Mo?ihega?i Island. — Lord. 
341 
less iron and magnesia than the olivine-noryte (I); while No. 
V, being chiefly pure diopside . VI contains over 7 per cent 
more iron and magnesia and nearly 16 per cent less AI2O3 than 
the same rock. It is of interest, further, to note that both of 
the derived rock-types are appreciably more acid than the 
noryte magma (I). 
The composition of the diopside (VI) from the gabbro- 
pyroxenyte (V) presents some interesting features which may 
be discussed somewhat more critically. For comparison the 
analysis of a grass green augite from the augite-phonolyte of 
the Cape Verde islands is given (VII).* Both these minerals 
contain an unusually high per cent of CaO+AUOs (34.26 and 
33.45) combined with but 42.55 and 43.99 SiO-s leaving only 
about 22% for the remaining elements. These facts indicate 
the presence of an alumosilicate (H.^ Al.^SiO«)* in the constitu- 
tion of the pyroxene, and enables the analysis to be interpreted 
as follows: 
SiO........ 26.62% 
FeO 6.74 
MgO 5-12 
CaO 12.50 
1 
50.99 
SiO. 6.78 
A1.03 11.52 
MgO 83 
CaO 515 
SiO. 
CaO 
MgO 
SiO^ 
K.O.. 
Na^O. 
Si02 
A 1.0. 
Na.O 
24.28 
4-39 
4.09 
2.93 
II. 41 
5 60 
3-75 
1.46 
10.81 
•47 
.20 
.12 
•79 
Ca (Mg, Fe) Si.Oo 
(Ca, Mg) AlsSiOo 
Ca Mg SiOs 
Na. Fe= Si40,= 
Na= Al: SiiOis 
^ 98.27 Pyroxene 
*See Naumann-Zirkel: Elemente der Min., 1898, p. 686. 
