228 
PACIFIC SCIENCE, Vol. XVIII, April 1964 
titanomagnetite nor hematite were visible as 
independent phases under the microscope. Tak- 
ing into consideration the thermodynamic equi- 
librium of the system, titanomaghemite in these 
rocks might be produced under a critical en- 
vironment. If we postulate a fixed temperature 
and oxygen partial pressure, then the composi- 
tion represented by the three components should 
also be fixed at the standard state. However, the 
study of stability relations did not reveal that 
titanomaghemite is experimentally stable at any 
temperature at a total pressure of 1 atmosphere. 
2. Comparison of Composition of Generalized 
Titanomagnetite with Japanese Calc-Alkali 
Rocks 
Recently, Akimoto and Katsura (1959) have 
studied the generalized titanomagnetite in Jap- 
anese volcanic rocks. From the data of analyzed 
specimens, we are able to pick out the titano- 
magnetites in a typical calc-alkali rock series 
ranging from basalt to rhyolite, and plot their 
compositions on the ternary diagram (Fig. 1). 
As will be seen in Figure 1, the compositions 
of titanomagnetites in Japanese calc-alkali rocks 
are arranged near the Fe.aOj-Fc^TiOi join, 
though there is some deviation from this line. 
Titanium content, in general, decreases with in- 
creasing differentiation. Thus, we find 20% 
TiO ; 2 in basalt, and 5% TiC >2 in rhyolite. In 
contrast, the generalized titanomagnetites in 
Hawaiian alkali-rich rocks are arranged nearly 
on the oxidation line, A-B. Of course, even in 
the Japanese calc-alkali rocks the titanomagne- 
tite is sometimes replaced by titanomaghemite, 
as described by Katsura and Kushiro (1961). 
Nevertheless, we were unable to find titano- 
maghemite as an extremely oxidized phase, as 
we did in Hawaiian trachyte and hawaiite. 
Typical titanomaghemites were found predo- 
minantly in alkali-rich olivine basalt, such as 
olivine analcite basalt from Atumi, and quartz- 
bearing olivine-titanaugite dolerite from Kin- 
goshi, Japan. The titanomaghemite found in 
Japan possesses almost the same composition as 
that of samples number 6 and 9 of this paper 
(Table 1). In consideration of this, titanomag- 
hemite seems to be more stable in alkali-rich 
rocks than in rocks of the calc -alkali series, re- 
gardless of the rock province in which they 
occur. 
REFERENCES 
Akimoto, S., and T. Katsura. 1959. Magneto- 
chemical study of the generalized titanomag- 
netite in volcanic rocks. Jour. Geomag. Geo- 
electr. 10:69-90. 
Basta, E. Z. 1959. Some mineralogical relation- 
ships in the system Fe 2 03 -Fe 3 04 and the 
composition of titanomaghemite. Econ. Geol. 
54:698-719. 
Darken, L. S., and R. W. Gurry. 1946. The 
system iron-oxygen, II. Equilibrium and 
thermodynamics of liquid oxide and other 
phases. Amer. Chem. Soc. Jour. 68:798-816. 
Katsura, T., and I. Kushiro. 1961. Titano- 
maghemite in igneous rocks. Amer. Mineralo- 
gist 46:134-145. 
, , S. Akimoto, J. L. Walker, 
and G. D. Sherman. 1962. Titanomagnetite 
and titanomaghemite in a Hawaiian soil. Jour. 
Sedimentary Petrol. 32:299-308. 
MacChesney, J. B., and A. Muan. 1959. 
Studies in the system iron oxide-titanium 
oxide. Amer. Mineralogist 44:926-945. 
Macdonald, G. A. 1949. Hawaiian petro- 
graphic province. Geol. Soc. Am. Bull. 60: 
1541-1596. 
I960. Dissimilarity of continental and 
oceanic rocks. Jour. Petrology 1:172-177. 
Powers, H. A. 1955. Composition and origin of 
basaltic magma of the Hawaiian Islands. 
Geochim. et Cosmochim. Acta 7:77-106. 
Taylor, R. W. 1961. An experimental study of 
the system FeO-Fe 2 O 3 -Ti O 2 and its bearing 
on mineralogical problems. Thesis in Dept, of 
Geophysics and Geochemistry, Pennsylvania 
State Univ. 
Tilley, C. E. 1950. Some aspects of magmatic 
evolution. Geol. Soc. London Quart. Jour. 
106:37-61. 
I960. Differentiation of Hawaiian ba- 
salts: some variants in lava suites of dated 
Kilauean eruptions. Jour. Petrology 1:47-55. 
Webster, A. H., and N. F. H. Bright. 1961. 
The system iron-titanium-oxygen at 1200° C 
and oxygen partial pressures between 1 atm. 
and 2* 10‘ 14 atm. Amer. Ceram. Soc. Jour. 
44:110-116. 
