Pyrolusite Concretions — SHERMAN, et al. 
121 
ited around very small nuclei. The size of the 
spherical concretions varies from barely visible 
specks to perfectly rounded balls three-eighths 
of an inch in diameter. The nature of the growth 
of these concretions prevents the inclusion of 
the surrounding soil. In general this type of 
concretion is scattered uniformly throughout the 
soil. The Concretions which form in root pas- 
sages, earthworm holes, cracks, and around soil 
aggregates have irregular shapes. These concre- 
tions are rough and have no definite shapes. 
Some of the concretions formed in this manner 
do include portions of soil. As mentioned be- 
fore, the concretions forming around roots have 
a tubular shape. They are irregular in length 
and diameter. When the root decays, the open- 
ing becomes filled with soil; however, the con- 
cretion will continue to grow with the gradual 
displacement of the soil from the opening. The 
three types of concretions are shown in Figure 1. 
The chemical composition of the mangani- 
ferous soil and its concretions was determined 
by procedures described by Piper (1944). The 
data obtained from this analysis are given in 
Table 1. The manganese oxide contents of the 
three soil samples are very variable; otherwise 
their chemical composition is quite uniform. 
The concretions have a very uniform composi- 
tion. The silica and iron oxide content of the 
concretions is lower than that of the soil. The 
alumina content of the concretions would sug- 
gest that they contain variable amounts of clay, 
which in the case of these soils would be of 
the kaolinite type. The Mn0 2 content of the 
concretions is uniform, varying from 27.9 to 
30.8 per cent. 
The data given in Table 2 were obtained 
from the analyses of typical concretions of the 
spherical, tubular, and irregular types. The chem- 
ical composition of the three types of concre- 
tions is in general similar. The total oxides are 
higher in the spherical form, suggesting either 
Fig. I. Types of pyrolusite concretions found in Hawaiian soils. Lower left, spherical type; 
upper center, tubular, formed around roots of plants (a black thread has been passed through 
the cavity left by a decayed root) ; lower right, the irregular type formed in the larger open- 
ings in the soil. 
