Kilauea lid. 1959'— MACDONALD and KATSURA 
363 
type. It is believed to be the olivine-enriched 
lower part of the last lava to spread across the 
crater floor. No phenocrysts other than olivine 
are present in any of the samples. The ground- 
mass is intergranular to intersertal, and consists 
of calcic plagioclase, averaging about An 65 , 
monoclinic pyroxene, iron ore, and locally inter- 
stitial glass. The pyroxene ranges from augite 
with an optic axial angle of at least 50° to 
pigeonite with an angle close to 0°. No silica 
mineral was observed. Glass increases gradually 
in samples below 15 ft., suggesting that inter- 
stitial fluid in the rocks was chilled at the time 
of sampling. 
Samples 9 and 10, the congealed liquid picked 
up in the end of the drill pipe, are much alike 
except for greater abundance of olivine pheno- 
crysts in the former. Both consist predominantly 
of glass. Around the edge a zone 1-2 mm. thick 
consists of about 85 per cent pale brown glass 
with scattered microlites of feldspar, pyroxene, 
and magnetite. This appears to have resulted 
from quick chilling of the liquid against the 
steel pipe. The rest of the core consists of black 
to deep brown glass, containing phenocrysts of 
olivine up to 1.5 mm. long, and small grains 
of plagioclase and pyroxene, locally clotted to- 
gether in glomeroporphyritic texture. The larger 
olivines have (— )2V = 80°=±i. They show 
moderate skeletal development, and little or no 
signs of resorption. The larger pyroxene grains 
are lime-poor augite, with ( + )2V = 50° ±. 
Some smaller grains have ( + )2V = 30° ±. 
Small grains of magnetite are present, and the 
dark color of the glass appears to result from 
very finely dispersed iron ore. The proportion 
of glass is variable, but averages 50-60 per cent. 
All but one of the Kilauea Iki samples are 
quite definitely tholeiitic. The single exception 
is sample 10, which is transitional from the 
tholeiitic to the alkalic rocks. In Figure 2, in 
which total alkali content is plotted against 
silica, sample 10 lies just within the alkalic 
FeO 
Fig. 1. Diagram of compositional variations in tho- 
leiitic rocks of the Hawaiian Islands. Large dots repre- 
sent the Kilauea Iki samples, the numbers correspond- 
ing with those in Table 1. Small dots represent other 
rocks. F represents the position of the iron-enriched 
segregation veinlet described by Kuno et al. (1957), 
and G indicates the position of the granophyre from 
Palolo Quarry, Honolulu, described by the same 
authors. 
basalt field. On the basis of very quick inspec- 
tion of the analyses, Dr. Kuno has suggested 
(oral communication, March 2, 1961) that 
sample 10 represents an iron- and alkali-enriched 
segregation similar to the veinlet from a flow 
in the wall of Kilauea caldera described by him 
and his associates (1957: 187). Indeed, in 
Figure 1 the point representing the iron-enriched 
segregation veinlet (F) lies directly on the trend 
of the Kilauea Iki rocks. However, the veinlet 
is distinctly poorer in alumina and richer in 
silica than Kilauea Iki sample 10, and lies well 
within the tholeiite field (Fig. 2). The similar- 
ity of Kilauea Iki sample 10 to typical alkalic 
basalts strongly suggests the possibility of de- 
rivation of the alkalic basalts in general from 
undersaturated tholeiitic magma. 
TABLE 1 ( Cont .) 
* Four careful determinations of each component in analysis 10 were made. The reproducibility (precision of measurement) 
is sufficient for the present purpose. Cu, Zn, V, Ba, Sr, Cr, Mo, W, and Pb were detected qualitatively by means of X-ray, but 
not in significant amounts, and cannot therefore be responsible for the low total in this analysis. The latter is the result of an 
appreciable amount of graphite in the analyzed sample, which was not soluble in mixed solutions of H2SO4 and HF or HNO3 
and HF. The graphite unquestionably came from the powdered graphite used to lubricate the joints of the drilling tools. The 
amounts of F, Cl, and C are being determined at the Tokyo Institute of Technology. 
