Generalized Titanomagnetite in Hawaii — KATSURA 
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tory, Kilauea; the same sample as that of Tilley 
(1950). 
No. 13. Sea sand; island of Molokai. 
Of these, samples 2, 10, and 12 belong to the 
alkali-poor tholeiite type, and the others are all 
of alkali-rich type. Indeed, the specimens of 
tholeiite type from which the ferromagnetic 
mineral was separated are scanty compared with 
those of alkali-rich specimens. However, as 
pointed out by Macdonald (1949) and Powers 
(1955), the chemical compositions of basalts 
belonging to the tholeiites series closely resemble 
each other if we take account of the amount of 
phenocrystic olivine and subtract it from the 
bulk. Thus the three samples of tholeiite studied 
in the present paper may reasonably represent 
Hawaiian tholeiite. 
The ferromagnetic fraction separated from 
sample 1 contained a small amount (at most 
10%) of the rhombohedral mineral, so the 
chemical composition of the spinel phase may 
be shifted to some extent to the side of the 
Fe 3 0 4 -Fe 2 Ti04 join as shown in Figure 1. The 
ferromagnetic fraction of sample 7 contained 
about 10% of hematite, so that the composition 
of the spinel phase may be moved toward the 
direction of high Ti0 2 along the join Fe 2 03- 
FeTiOs, as will be seen in Figure 1. 
Fig. 1 . Composition of generalized titanomagnetites 
represented on a FeO - F esO 'a— TiO 2 diagram. Solid 
circles represent the generalized titanomagnetites from 
Hawaiian rocks, and open circles, titanomagnetites 
from Japanese calc-alkali rocks. (Meaning of arrows 
is explained in the text.) N. B, : right side of triangle, 
for FesTiOs read FeTTlO-,.. 
RESULTS AND DISCUSSION 
1. Composition 
Table 2 shows the chemical composition of 
the generalized titanomagnetite, and Figure 1 
is a ternary diagram based on the components 
FeO, Fe20s, and Ti0 2 . In Figure 1 a line, A-B, 
indicates the oxygen reaction line when material 
of composition A is oxidized to a final composi- 
tion B. In a previous work, Katsura, Kushiro, 
Akimoto, Walker, and Sherman (1962) pointed 
out that the Hawaiian titaniferous ferruginous 
latosol enriched in iron and titanium has origi- 
nated from titanomagnetite in volcanic rocks, 
and deduced the original composition of titano- 
magnetite from which a latosol of Naiwa type 
on the island of Kauai must have been formed. 
The chemical composition of this titanomag- 
netite lies just on the oxidation line A-B. 
It is clear from Figure 1 that the compositions 
of titanomagnetite and titanomaghemite in Ha- 
waiian volcanic rocks lie near the line A-B; 
and also we realize that the compositions of 
numbers 9, 13, and 7, which deviate somewhat 
from the line, represent the typical titanomag- 
hemite studied by Basta (1959), and Katsura 
and Kushiro (1961). 
In a series of Hawaiian volcanic rocks of 
alkali-rich type, the compositions of the gen- 
eralized titanomagnetites are safely interpreted 
as resulting from either oxidation or reduction 
of material of a composition on or near the line 
A-B. In detail, for instance, number 1 is an 
oxidized phase of number 11, both rocks be- 
longing to the upper Waianae series on Oahu; 
and number 8 is a reduced phase of number 6, 
both belonging to the Honolua series on West 
Maui. 
Titanomagnetite separated from the reheated 
picrite basalt contained a significant amount of 
chromium, as shown in Table 2. In addition to 
this, according to Ramdohr the opaque mineral 
in this rock is surrounded by magnesioferrite. 
Thus, the titanomagnetite in the reheated basalt 
is much different in its constituents from that in 
common Hawaiian basalts. 
It should be noted again, though already 
pointed out in this paper, that the generalized 
titanomagnetite is extremely oxidized to form 
typical titanomaghemite in the trachyte (No. 
6) and hawaiite (No. 9), in which neither 
