Mineralogy of 

Selected Soils 

from Guam

GEOLOGICAL SURVEY PROFESSIONAL PAPER 403-F
Mineralogy of 

Selected Soils 

from Guam

By DOROTHY CARROLL and JOHN C. HATHAWAY

with a section on

DESCRIPTION OF SOIL PROFILES

By CARL H. STENSLAND

GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

GEOLOGICAL SURVEY PROFESSIONAL PAPER 403-F

A mineralogical study of selected soil samples of 

Guam, including data on chemical composition, 

grain-size distribution, and comparison with other 

areas, as well as a description of soil profiles

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.G., 20402
CONTENTS

Abstract____________________________

Introduction __________________________

Outline of geology_-------_---_---_--_-

Soils of Guam_________-___-_-_---_--_-

Methods of examination._______________

Mechanical analysis______________

Chemical analysis________________

Mineralogical analysis ____________

Results of analyses___________________

Mechanical composition ____________

Soil reaction. _____________________

Chemical composition______________

Atate clay on volcanic rocks _ _ _ _ Asan clay on volcanic rocks_____

Guam clay on limestones _______

Fossil red latosol_____________

Chacha clay on limestone_______

Chemical characteristics--______

Free iron oxide________-__________.

Ion-exchange capacity______________

Organic matter____________________

Mineralogical composition__________

Sand fractions_______________

Clay and silt fractions_________.

Soil genesis.__________________________

Evidence from chemical composition.

Soils on volcanic parent rocks. _.

Silica removal____________.

Alumina accumulation___.

Page 

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12

13

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18

24

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27

27

Page 

Soil genesis Continued

Evidence from chemical composition Continued 

Soils on volcanic parent rocks Continued

Ferric oxide____________________________ F28

Titania__ _____________________ 28

Water. ________________________________ 29

Soils on limestones__________________________ 29

Silica__________________________ 29

Alumina,_ _____________________________ 30

Ferric oxide____________________________ 30

Titania__________________________ 30

Phosphate. ________________________ 30

Evidence from mineralogical composition __________ 30

Soils on volcanic rocks_______________________ 30

Soils on limestones__________________________ 32

Comparison of soils of Guam with those of similar parentage in other selected areas______________________ 36

Volcanic rock soils______________________________ 36

Hawaiian Islands___________________________ 36

Norfolk Island_______________________ 36

Lismore, New South Wales__________________ 38

Inverell, New South Wales_______________ 38

Antrim, Northern Ireland__________________ 38

Soils on limestones______________________________ 39

Conclusions ________________________________________ 40

References.-..______ _______________________________ 41

Description of soil profiles, by Carl H. Stensland______ 43

Soils on volcanic rocks_________________________ 43

Soils on limestone__ ___________________________ 48

Index.________-_-____---_--------_--__---_------__ 51

ILLUSTRATIONS

Page

FIGURE 1. Parent rocks of soils on Guam, andesite, basalt, tuffaceous sandstone, and weathered tuff____________________ F4

2. Parent rocks of soils on Guam, pillow basalt-_________-__--_-_-_-___---_---_--_-.------_---------------- 5

3. Localities of soil profiles on Guam_______________________._____-___---_---__--_-_-_---_------_-------- 6

4. Heavy residues of sand fractions of soils on Guam__________-___-___-_-_--__---_-_-_---_-__-----___--_- 16

5. Diagram showing proportion of halloysite to gibbsite and boehmite in the various soil profiles- _____________ 21

6. Differential thermal analyses of clay «2ji) from soils developed on limestones and on volcanic rocks _____ 22

7. Diagram showing percentage of goethite and hematite in the various soil profiles_____-__--__--__---_---_--- 24

8. Chemical composition, recalculated on water-free basis, of profiles of Atate clay and Asan clay on volcanic rocks. 28

9. Diagram showing mineralogical relationships of soils developed on basaltic materials in various localities ____ 33

TABLES

Page 

TABLE 1. Calcium carbonate, magnesium carbonate, and insoluble residues of limestones from Guam_________-__------_ F2

2. Chemical composition of the volcanic rocks of Guam________-_______-___---___-_---_---_---_----------- 7

3. Mechanical composition and pH 6f soils on volcanic rocks and on limestones-____--_----_-_-_--------------- 8

ni
IV CONTENTS

Page 

TABLE 4. Major chemical constituents in samples of soil from 13 soil profiles on Guam________________________________ F10

5. Organic carbon, free iron oxide, and ion-exchange capacity of soils on volcanic rocks and on limestones.________ 12

6. Heavy minerals (sp gr >2.8) in the sand fractions (0.25-0.10 mm and 0.10-0.05 mm) of soils from Guam______ 14

7. Mineralogy of the clay and silt fractions of soils.___-_______-_____---_-_---_---___----__----_____________ 18

8. Interpretation of thermal reactions shown by differential thermal analysis curves in figure 6_-___-___-_____-__ 20

9. Average chemical composition of three groups of volcanic rocks that are parent materials of soils on Guam._ __. 25

10. Average chemical composition (water-free basis) of soil profiles developed on volcanic rocks and on limestones

from Guam____________________-_____________-_______-_-___---__---____--__-_--__-_-___--_________ 25

11-15. Chemical composition of parent rock and soil profiles:

11. Atate clay on Alutom Formation (profile S54-4)_______--_-___-----__-_-_____-__-_____________-____ 25

12. Atate clay on Alutom Formation (profile S54-5)____-_--__-__-__-_--_-__--__-_-_____-______________ 26

13. Atate clay on Bolanos Pyroclastic Member of the Umatac Formation (profile S54-6)___________________ 27

14. Atate clay on pillow basalt of the Facpi Volcanic Member of the Umatac Formation (profile S54-12)_____ 27

15. Asan clay on Alutom Formation (profile S54-23) _____ ______________________________________________ 27

16. Normative clay mineral composition, calculated from chemical analyses, of soil profiles on volcanic rocks and on

limestones- ----____--__-__-__-_______-_____-__----_---------_------__----.__----____-___---_-_--__- 29

17. Changes in chemical composition of the Guam clay (average), presuming that it developed from material similar

to the Chacha clay________--_____________________-_--____-____-__-_____--______-_-_-_________---__ 30

18. Weathering sequence of minerals in rocks and soils of Guam. _____________________________________________ 31

19. Comparison of soils developed on basalt and volcanic ash from various selected localities._____-_________--_-_ 37
GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

MINERALOGY OF SELECTED SOILS FROM GUAM

By DOROTHY CARROLL and JOHN C. HATHAWAY

ABSTRACT

Data are given for the grain-size distribution, pH, chemical 

composition, organic carbon, free iron oxide, ion exchange capacity, and mineralogy of soil samples from 14 profiles on Guam. 

Six of the profiles are developed on limestone and eight on volcanic rocks. Most of the soils are described as red latosols and 

are clayey. The principal soil overlying volcanic rocks, the 

Atate clay, averages 71 percent clay, 23 percent silt, and 6 percent sand. The principal soil overlying limestone, the Guam 

clay, averages 59 percent clay, 33 percent silt, and 9 percent 

sand. In chemical composition the Atate clay averages 35.5 

percent SiO2, 27.9 percent Al2 0a, 14.5 percent Fe2 O3 , and 1.0 

percent TiO2 . The Guam clay averages 1.4 percent SiO2 , 39.1 

percent A12 O3 , 20.9 percent Fe2 03 , and 2.0 percent TiO2 . Comparison of the SiO2 percentages for weathered rock and surface 

soil of the Atate clay show that silica has been removed during 

development of the profile. Alumina and ferric oxide accumulate 

in these soils.

Normative mineral compositions of representative soil profiles 

show that a kaolin mineral, goethite, and a little gibbsite make 

up the bulk of the Atate clay; whereas gibbsite, hematite, and 

a little kaolin mineral are the main "constituents of the Guam 

clay. X-ray diffraction and differential thermal analysis identify 

the kaolin mineral as halloysite.

The pH of the Atate clay averages 5.3; that of the Guam clay, 

7.4. Other soils have intermediate pH values.

The percentage of free iron oxide, defined as that readily 

removed and not combined in minerals, shows considerable 

variation both within the individual profiles and between the 

profiles. The Atate clay averages 12 percent free iron oxide, 

and the Guam clay 18 percent free iron oxide. Other soils have 

as little as 4 percent.

The surface soils contain, on the average, 3.5 percent organic 

carbon and about 6 percent organic matter. The cation exchange capacity of these soils ranges from 7 to 24 milliequivalents per 100 gram, the capacity being highest near the surface 

owing to the presence of organic matter.

The minerals in the sand fractions are magnetite, ilmeiiite, 

indefinite red and black iron oxides, augite, hypersthene, green 

and brown hornblendes, and a very small quantity of other 

minerals, such as zircon and sphene. Magnetite makes up half 

to more than three-fourths by weight of the heavy minerals. 

Ilmenite is abundant in some samples. Augite and hypersthene 

are variable in amount and commonly are concentrated in the 

surface soils. Grains of these minerals are fresh in the soils on 

limestone, but they are generally corroded in soils formed from 

volcanic rocks. The minerals in the silt and clay fractions are 

halloysite, montmorillonite, mixed-layered montmorillonitehalloysite, goethite, hematite, gibbsite, boehmite, a-cristobalite, 

anatase, chromite, and weddelite. The most abundant of these 

minerals are halloysite, goethite, hematite, and gibbsite.

The principal weathering process in the development of the 

Atate clay is the removal of silica and the consequent accumulation of alumina, iron oxide, and titania. The Guam clay has a 

more complex genesis as the limestones beneath it vary in their 

content of insoluble residue and in the kinds of minerals present. 

In some limestones the residue consists principally of fresh volcanic ash minerals, but in others, soil material from the erosion 

of land surfaces is present.

The soils developed on volcanic materials on Guam are compared with other lateritic soils and with fossil laterites. Soils 

thus compared are from the Hawaiian Islands, Norfolk Island, 

Australia, and Northern Ireland. The clay minerals of all these 

soils show a progressive change from montmorillonite > 

halloysite * kaolinite » gibbsite. The Atate clay of Guam 

is a uniform profile that apparently has not reached the same 

stage of development as have the older soils of the Hawaiian 

Islands. The ease of the weathering of the tuffs on Guam that 

contain zeolites and glass suggests that these soils have developed more rapidly than similar soils 011 compact basalts and 

andesites. The soils overlying limestones are compared with 

terra rossa type soils of other Pacific islands, the West Indies, 

and the bauxites of Hungary.

INTRODUCTION

Guam lies about 13° north of the Equator in the zone 

of tropical weathering and soil formation. The island 

consists of volcanic rocks (largely andesitic in composition) and limestones. The soils are lateritic. Deposits 

of red earthy material on the limestones appear to be 

similar to the terra rossa deposits of the Mediterranean 

region, Jamaica, and some islands in the Pacific.

During the mapping of the soils on Guam by Carl H. 

Stensland, assisted by James E. Paseur, U.S. Geological 

Survey, it became evident that much information concerning the origin and development of the soils could 

be obtained by detailed mineralogical and chemical 

analyses. Subsequently, Stensland selected 14 soil 

profiles for further investigation and 70 samples were 

collected. Six of the soil profiles overlie limestone and 

eight overlie volcanic rocks. The soils are mostly 

residual red latosols; but the surface material may be 

truncated, or other material may have been added to 

it. There are 5 profiles of Guam clay above Mariana 

Limestone, 1 profile of Chacha clay on the Agana 

Argillaceous Member of the Mariana Limestone, 7 

profiles of Atate clay on various types of volcanic rocks, 

and 1 profile of Asan clay on volcanic rock.

Fl
F2 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

Differential thermal analyses were made of some 

soils during the course of fieldwork on Guam by means 

of a small portable unit, and subsequently, seven 

samples were analyzed by George T. Faust, U.S. 

Geological Survey, using laboratory equipment.

At almost the same time that these soils were submitted for analysis, we were asked to study the insoluble 

residues of selected samples of limestone from Guam 

to aid petrographic description (Schlanger, 1963). Information from this study is used here in discussing the 

origin of the soils overlying limestones.

Data are given in this chapter on the grain-size 

distribution, pH, chemical composition (including complete analyses for a number of soil profiles), free iron 

oxide, exchange capacity, and mineralogy of the sand, 

silt, and clay fractions. X-ray examination of the silt 

and clay fractions showed the distribution of the various 

clay minerals within the soil profiles.

The soils of Guam are compared mineralogically and 

chemically with lateritic soils and terra rossa deposits 

that have developed on similar types of rocks in other

places.

OUTLINE OP GEOLOGY

Geologically and topographically Guam is divided 

into two parts: a northern plateau of limestone ranging 

in age from Eocene to Pleistocene, and a southern 

hilly region consisting of lava flows and associated 

tuffs and agglomerates (Tracey and others, 1963). 

The limestones of the northern plateau rest unconformably on volcanic rocks, the Alutom Formation. The 

Mariana Limestone is the most prominent formation. 

All the limestones vary in content of insoluble detrital 

material that has been derived from the weathering of 

the volcanic rocks or from ash falls during deposition 

of the limestone.

Chemical analyses of selected limestones having sufficient insoluble residue for optical and X-ray examination are given in table 1. The percentages of insoluble 

residue may not be the average or the range characteristic of each formation.

The mountainous central core of the island consists 

of the Alutom Formation, a succession of more than 

2,000 feet of folded and faulted marine tuffaceous shale 

and sandstone, lava flows, limestone, and conglomerate 

of Eocene and Oligocene age. The Mahlac Member 

of this formation consists of shale and sandstone and 

contains planktonic Oligocene Foraminifera. The 

southern third of the island is a succession of eastwarddipping volcanic rocks and limestones about 2,200 feet 

thick, which is termed the Umatac Formation and 

comprises four members: the Facpi Volcanic Member, 

the Maemong Limestone Member, the Bolanos 

Pyroclastic Member, and the Dandan Flow Member.

TABLE 1. Calcium carbonate, magnesium carbonate, and insoluble 

residues of limestones from Guam

[Analysts: J. L. Dinnin, P. W. Scott, and H. F. Phillips, U.S. Geol. Survey. Given

to percent]

Sample

Mariana Liirestone, detrital facies: 

Sw 2-4- _ .__ ........

Pr 3-3.... ....... .....................

Kr 3-1 _-_ _ ..........

Agajia Argillaceous Member: 

l]Z-l........ .........................

Barrigada Limestone: 

Nq 15-1 ________ _____ . ....

Alifan Litrestone: 

Ru8-3-. _.

Di 2-1.. _- 

Di 2-2.. ........ _ -.-.-.....-.-......

Tsft-1 - _ - _ _ 

J13-2 ... _ .....................

Janum Formation: 

Ts 5-4.......... ......................

Ts ^-0.. ..............................

Rr 23-1

Rr5-l . ... _ -__. _ - 

Bonya Limestone: 

Ut 6-1 . ..

Rrl3-l- _ . -.-. _ 

Gi2-l. 

Urratac Formation, Maemong Limestone 

Member: 

Gil-2a._.__._...._... ...-...-.-.-.-..

Efl-1 _ ..... ___ ..... _ ...........

Ed 1-lb - ........................

Ee 2-1 . _._-_ _ 

Df9-la_. ....... ______________________

li 5-2 ..............................

Alutom Formation: 

Fk 4-ll__-.__. _ . ._. -.

Mahlac Shale Member: 

Gj 11-1-- -- .--.- ..... ....

CaCOs

65.86

98.53

96.03

88.89

98.17

96.74

98.88

81.75

97.63

88.53

95.14

98.17

97.63

98.17

91.03

98.17

96.39

74.07

78.36

99.24

97.85

52.65

MgCO3

1.04

1.08

1.04

1.04

1.73

1.75

1.04

1.63

1.50

1.21

.98

1.69

1.38

1.59

1.57

1.80

2.72

2.50

1.27

.85

1.79

.52

Insoluble 

residue

01 o

.9

.1

3

K

. 1

10.0

1.1

7.5

1.9

.3

14.2

1.0

9.8

3.6

0.9

1.4

.5

7.4

.3

1.6

23.8

20.8

.7

1.0

42.4

The oldest volcanic rocks, the Alutom Formation, 

are characterized by abundant white and light-gray 

tuffaceous shales which are water-laid pyroclastic sediments. Interbedded with these sediments are lava 

flows and agglomerates and breccias of volcanic material. Where fresh, the tuffaceous rocks are calcareous, 

but surface exposures have become silicified. Weathering results in the removal of the calcareous cement, and 

a soft clayey rock remains.

The Umatac Formation contains more basalt flows 

and less tuffaceous material than the Alutom Formation. At the base the Facpi Volcanic Member of the 

Umatac Formation is as much as 1,400 feet thick and 

consists of mafic lava flows, pillow basalts and dikes, 

and in some places water-laid tuff and conglomerate. 

Both the Bolanos Pyroclastic Member and the Maemong Limestone Member are water laid and contain 

volcanic material. All are deeply weathered.

The volcanic rocks of Guam, more andesitic in 

character than those of the Pacific basin, resemble rocks 

of the Pacific margin (Stark, 1963). They range in 

type from basalt and olivine basalt to andesite, with 

more than 50 percent mafic andesite; only a very minor 

percentage are dacites. Thin sections of some of these 

rocks are shown in figures 1 and 2.
MINERALOGY OF SELECTED SOILS P3

Chemical analyses of samples of these mafic rocks 

are given in table 2.

The minerals present in the volcanic rocks (Stark, 

1963) are plagioclase feldspars and pyroxenes (augite 

and hypersthene); olivine and quartz are present but 

are not abundant. Primary accessory minerals are 

magnetite, hornblende, biotite, alkalic feldspar; secondary and alteration minerals are chlorites, serpentines, 

epidote, calcite, zeolites, celadonite, opaline silica and 

clay minerals. The most abundant of these minerals is 

plagioclase feldspar, followed by monoclinic pyroxene 

(largely augite); olivine is rarely fresh, its place having 

been taken by pseudomorphs of serpentine, chlorite, or 

calcite; hypersthene occurs only in a few samples.

As the parent material of soils, the most important 

feature of these mafic rocks on Guam is the almost 

complete absence of minerals that are resistant to 

weathering processes. These rocks are generally altered 

to clays, and weathering frequently extends to 100 feet 

below the surface.

The relation between volcanic rocks and limestones, 

the types of volcanic rocks, and the insoluble residues of 

the limestones of Guam are similar to those described 

for the Lau Islands, Fiji, by Ladd and Hoffmeister

(1945).

SOILS OF GUAM

Numerous soil units were mapped by Carl H. 

Stensland. These include the following associations of 

upland soils on limestone and volcanic rocks.

Upland limestone soils Description

Guam clay_____________ Reddish friable permeable clay; generally less than 12 in. deep.

Toto clay______________ Pale-yellow firm plastic clay with

reddish stains; slowly permeable; 

generally deep.

Chacha-Saipan clays___- Yellowish-brown firm clay (Chacha)

and red firm clay (Saipan), mediumdeep to deep.

Soils of unit 3 with a shallow brownish 

clay (Yona) on convex slopes.

Yona-Chacha clays____ Shallow (Yona) clay on upper ridge

slopes and deeper yellowish-brown 

(Chacha) clay on toe slopes and in 

basins. 

Upland volcanic soils

Atate-Agat clays, rolling. Red granular porous acid clay (Atate)

associated with small benchlike 

mesitas, and a truncated latosol 

(Agat clay) with solum almost all 

removed; red staining and reticulate 

mottling deep into C or saprolitic 

horizon (the saprolite is in most 

places 50 ft or more thick over 

relatively unweathered rock). 

Atate-Agat clays and a truncated 

latosol (Asan clay) with very little 

staining or red mottling.

Saipan-Yona- Chacha 

clays.

Agat-Asan-Atate clay, 

hilly.

Upland volcanic softs

Agat-Asan clays and rock 

outcrop.

Description

Agat and Asan clays less .deeply 

weathered or more truncated with 

some rock exposures.

The Guam clay, although relatively thin, has the 

greatest areal extent of any of the soils on Guam, as 

it covers the limestone plateau on the northern half of 

the island. The other types of limestone soil the 

Toto, Chacha, Saipan, and Yona clays are developed 

on the northeastern and eastern slopes of the higher 

southern part of the island where they flank the 

volcanic material.

The soils developed on the weathered volcanic rocks 

of Guam occur principally in the southern half of the 

island. The weathering of the marine tuffaceous shales 

and associated rocks, and of the andesitic or basaltic 

lava flows, extends to an average depth of 50 feet. 

The weathered rock is similar in appearance to the 

saprolite of the southeastern United States; that is, 

the original textures and structures of the rocks are 

preserved although the fresh minerals have been replaced by clay. The volcanic parent materials have 

similar chemical composition; so the principal differences in these soils can be attributed to topography and 

age. Both regosols (Chacha and Asan clays) and 

latosols (Guam and Atate clays) are present.

The following samples of soil from profiles developed 

on limestone and on the volcanic rocks were collected 

by Carl H. Stensland for the investigation.

Soil profiles on limestone

S54-16 Guam clay on Barri- S54-4

gada Limestone. 

S54-17 Guam clay on S54-5

Mariana Limestone. 

S54-18 Guam clay on S54-6

Mariana Limestone.

S54-19 Guam clay on S54-10 

Mariana Limestone.

S54-24 "Fossil" latosol on S54-12 

Alifan Limestone.

S54-1 Chacha clay on S54-20 

Agana Argillaceous 

Member of the S54-21 

Mariana Limestone.

S54-23

Soil profiles on volcanic rocks

Atate clay on Alutom 

Formation.

Atate clay on Alutom 

Formation.

Atate clay on Bolanos 

Pyroclastic Member 

of Umatac Formation.

Atate clay on Bolanos 

Pyroclastic Member 

of Umatac Formation.

Atate clay on Facpi 

Volcanic member 

of Umatac Formation.

Atate clay on Alutom 

Formation.

Atate clay on Alutom 

Formation.

Asan clay on Alutom 

Formation.

Details of these profiles are given in the description 

of soils by Stensland (p. F43-F49). Locations are 

shown on figure 3.)
A. Basic flow, calcic andesite. Phenocrysts of augite and zoned feldspars in a matrix 

of plagioclase, pyroxene, glass, magnetite, zeolites, and alteration products. 

Ordinary light, X 35. Mount Santa Rosa.

B. Basic flow (Ee 4-2), basalt, near Umatac springs. Plagioclase and augite in a 

groundmass of plagioclase, pyroxena, and glass, with zeolites. Ordinary light, 

X13.

I*

C. Water-laid tuffaceous sandstone (Fo 6-1), Alutom Formation, Spruance Drive. 

Plagioclase, altered augite, devitrifled glass, clay and chloritic minerals. 

Crossed nicols, X 35.

D. Water-laid tuff altered to red clay in place, Sasa Valley. Some fresh plagioclase, 

altered pyroxenes, magnetite, and clay minerals. Ordinary light, X 7.

FIGURE 1. Parent rocks of soils on Guam.

METHODS OF EXAMINATION

Mechanical, chemical, and mineralogical examinations 

were made on the soil samples of the profiles developed 

on limestone and on volcanic rocks in order to provide 

the information required to describe these soils and 

their development from the underlying rocks. In 

addition, use was made of petrographic descriptions

of thin sections of the limestones (Schlanger, 1963) and 

of the volcanic rocks (Stark, 1963).

MECHANICAL ANALYSIS

The grain-size distribution for aE the samples was 

obtained by the standard procedure for mechanical 

analysis of soil (Kilmer and Alexander, 1949, p. 15). 

This method consists of dispersing the soil with sodium
MINERALOGY OF SELECTED SOILS F5

M

A. Weathered pillow basalt (Ch 3-1), old road to Pacpi Point. Plagioclase, augite, 

celadonite apparently replacing zeolites, saponite within the radiating celatlonite, altered glassy groundmass. Ordinary light, X 34.

B. Same as A, but with crossed nicols.

FIGURE 2. Parent rocks of soils on Guam.

metaphosphate, removing the sand grades with sieves, and 

determining the amount of silt and clay by pipette analysis. The analyses were made by Paul D. Blackmon, U.S. 

Geological Survey.

CHEMICAL ANALYSIS

The major constituents of 46 samples of soil representing 13 profiles were determined by rapid analysis 

methods under the supervision of W. W. Brannock, 

U.S. Geological Survey. Many of the surface samples 

contained organic matter which interfered with the 

methods used and caused low total figures as shown in 

table 4.

Organic carbon was determined in the surface samples 

from the profiles by Walkley and Black's rapid titration 

method (Piper, 1947, p. 223) which consists of oxidation of the carbon in the organic matter by potassium 

dichromate. The results obtained give 80 to 90 percent 

of the organic carbon present. Multiplying the figures 

by 1.72 gives an approximation to the total organic 

matter present.

The free iron oxide (Fe2O3) on the mineral grains of 

the whole soil was determined by a modification of 

Deb's method (1950, p. 212), which consists of the removal of ferric oxide by reduction to ferrous oxide with 

sodium hydrosulfite (dithionate) Na2S2O4-2H2O. The 

iron in solution was determined colorimetrically using 

potassium hydrocyanite.

677-184 O 63 2

The t3tal cation exchange capacity of the whole 

soils was determined by Bower and Truog's colorimetric 

manganese method (1940), in which the exchangeable 

cations are replaced by manganese which is, in turn, 

replaced by ammonium as ammonium acetate. The 

amount of manganese equal to the exchangeable cations 

is then determined colorimetrically with a spectrophotometer.

MINERALO GIG AL ANALYSIS

Sand grades. From the grain-size distribution of 

these soils (table 3) it is seen that very little material 

coarser than silt (0.05 to 0.002 mm) is present. It was 

therefore necessary to concentrate the sand from large 

samples of soil to obtain sufficient minerals for examination. The clay was removed by washing and decantation, leaving the coarsest material which was then 

boiled in 1:1 hydrochloric acid, washed, dried, and 

sieved into fractions of the same size as those of 

the mechanical analysis. The 0.25- to 0.10-mm and 

0.10- to 0.05-mm sand grades were separated in bromoform, the magnetite removed and weighed, and the 

remaining heavy minerals mounted in Canada balsam 

for microscopic identification.

Silt and clay grades. The material passing the 270- 

mesh sieve in the mechanical analysis procedure was 

separated into silt and clay fractions and examined by 

X-ray diffraction, using the methods described by 

Hathaway (1956) and Hathaway and Carroll (1963).
F6 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

Go 10 

Fo 6. .L.S-54-4

 /fGo 7 S-54-23

Gm 33 . 

Gm 5 J;Gm 9

/Gm 21. 25

EXPLANATION

AS-54-18 

Soil sample and number

.Ru 8 

Rock sample and number

3 MILES

FIGURE 3. Localities of soil profiles on Guam.
MINERALOGY OF SELECTED SOILS P7

TABLE 2. Chemical composition, in percent, of the volcamc rocks of Guam

[Samples Ee 4-2c, Fd 2-lb, Go 7-lc, Go 7-ld, Dh 6-lb, Dh 6-lc by rapid methods; analyzed by H. F. Phillips, P. L. D. Elmore, K. E. White. Samples Df 2-1, Ee4-2, Fd 

2-1, Fo 10-1, Go 7-1, le 2-1, Go 10-2, If 6-1, Ch 4-3, Ch 4-4, Gm 1-2, Gm 25-1, Go 6-1, le 3-1 analyzed by E. J. Thomasi. Samples Ss 9-1, Fm 2-1, Gm 9-1, Gm 21-1, Qm 

33-1, Gm 5-la, Gm 5-lb, Gm 5-lc analyzed by L. D. Trumbull]

Sample SiO2 A12O3 Fe2O3 FeO MgO CaO Na2O K2O H 2 O- H 2 0 + TiO2 CO2 P2 05 MnO Total

A. Basalt and other lava flows

Ee 4-2c _ ______

Fd 2-lb______-__

Go 7-lc_ .__--__

Go 7-ld________

Df 2-l______--_-

Ee 4-2___ ______

Fd2-l____--_--_

Fo 10-1___ _

Go 7-1---- 

Dh 6-lb_._ _____

Dh6-lc___ _____

51.7

54. 1

53. 5

47. 7

50.85

52.09

53. 19

48.48

48. 58

55.0

54. 2

14.6

14.8

14. 9

15.6

13. 55

15. 81

17. 51

15.99

16. 53

13.8

14.6

4. 5

4.7

3. 7

46

2. 24

3. 71

1.61

3.69

3. 39

3.8

5. 1

7.9

6. 1

3. 2

3.8

5. 43

7.81

7. 16

4.64

3. 74

4.0

3.4

4.7

3.7

7.0

9.0

10.01

429

3.97

8.93

8. 55

9.4

8.0

9. 1

8.0

7.8

10.3

9.55

9.44

9.20

10.90

9. 88

7.9

7.9

2.6

2.8

2.9

2.0

1. 58

2.48

2.71

1 80

2. 01

2. 3

2.4

0.70

.82

.62

. 36

. 16

.76

.94

. 14

.45

. 88

1.4

1 3.0

1 3.8

1 5. 4

i 5.8

4 13

1. 18

. 85

2. 83

3. 95

1 2.6

1 2.9

1. 91

1. 12

1.25

1. 91

1.93

0.92

1.0

. 50

. 54

.34

.97

1.04

.57

.62

. 34

. 36

<0.05

<.05

.50

.05

.07

.01

.01

.00

.00

<.05

<.05

0.25

.26

. 10

.08

.03

. 24

.26

.07

.09

.07

.08

0.20

. 15

. 12

. 13

. 14

.20

. 19

. 14

. 13

. 11

. 12

2 100

2 100

2 100

2 100

99.99

100. 11

99.89

100. 09

99.85

2 100

2 101

B. Dikes cutting mafic flows and boulders in conglomerates and pyroclastic agglomerates

le 2-l__________

Go 10~2-_______

If 6-1. _________

Ss 9-l_._ _______

Ch4-3__ _______

Ch 4-4___ ______

Gm 1-2 _______

Gm 25-1 _ _____

Go6-l_________

Ie3-l_ _

55.73

65. 19

60.02

68.89

51. 63

53. 53

64 49

58. 43

69.04

51.06

19. 50

15.65

16. 74

13. 73

14 10

16.28

14 01

14 80

12. 71

18. 05

2.56

2. 54

3. 50

2. 59

2. 27

2. 53

1. 62

1. 82

3. 20

3.63

4 59

2.04

3. 31

1. 70

5. 93

5. 24

2. 19

5. 10

1.03

6.08

1.98

2.41

2.86

2. 11

9.93

5.41

3. 23

6. 58

1.96

4.56

8.03

5.36

6.67

4.42

q 47

5.59

7.73

7.77

5.79

10.09

3.24

3.29

3. 35

3.50

2.21

5. 14

2. 65

2. 57

2. 50

2.45

2. 14

1. 04

1. 52

1.00

. 52

1. 77

.80

.54

1.00

1. 02

0.26

. 72

.65

. 77

1. 84

1. 09

.86

.73

1. 23

. 81

0.75

1.08

.30

.95

1.42

2.45

.69

.93

.81

. 71

0.67

. 44

. 56

.23

. 43

. 60

.39

. 50

. 36

.73

0. 02

. 01

.01

.07

.07

. 11

.94

.02

.09

. 15

0. 36

. 11

. 19

.05

.05

.08

.08

.08

.05

. 22

0. 15

.06

. 13

.05

. 15

. 12

.08

. 14

.05

.20

99. 98

99. 94

99.81

100. 06

100. 02

99. 94

99.76

100. 01

99.82

99. 76

C. Tuffs and weathered tuffs

Fm 2-1 _____ _

Gm 9-l__ _ _ _

Gm 33-1

Gm 5-la- __ ___

(r"rn > 1 c

73. 58

7409

70. 59

52. 88

67. 10

7423

47. 78

9.68

10.23

10.05

23.95

13.07

14 36

26.23

1. 14

.73

1. 30

7.76

2. 34

1. 42

5.43

0. 14

. 12

. 18

.00

. 64

. 16

. 07

0.48

.47

1.38

1. 13

1.42

. 18

2.03

1.98

2.94

2.42

.00

1.63

. 17

.31

1.37

1.67

.35

.06

1. 22

. 10

.06

0.82

. 55

1. 12

. 98

1. 19

. 20

. 12

4.07

3. 77

4.61

2. 73

3. 88

2. 50

6. 59

6. 16

5.20

7.47

9. 31

6. 74

5. 91

10.58

0.21

. 23

. 39

.74

. 21

.34

. 37

0.01

. 01

.01

. 15

.00

.01

.01

0.00

.02

. 01

.06

.20

. 14

. 15

0.02

.01

.01

.27

.05

.02

.02

99 66

100. 04

99.89

100. 02

99.69

99. 74

99.75

1 Total H2O.

2 Total as reported by the analysts.

Sample no. DESCRIPTION OF SAMPLES

Ee 4-2c Basalt lava flow near middle, above Umatac springs.

Fd 2-lb Basalt lava flow near top, above Merizo dam.

Go 7-lc Basalt lava flow near top, Spruance Drive roadcut.

Go 7-ld Basalt lava flow near bottom, Spruance Drive roadcut.

Df 2-1 Mafic flow, old road to Umatac, west of Latti stones.

Ee 4-2 Mafic flow over pyroclastics, above Umatac springs.

Fd 2-1 Mafic flow 520 ft upstream from road above Merizo dam.

Fo 10-1 Mafic lava flow, Spruance Drive roadcut.

Go 7-1 Mafic lava flow, Spruance Drive roadcut.

Dh 6-lb Mafic flow near base, slightly weathered, Lamlam roadcut.

Dh 6-lc Mafic flow near top, slightly weathered, Lamlam roadcut.

Ch 4-3 2-ft dike cutting mafic flows, 3,600 ft northeast of Facpi Point.

Ch 4-4 4-ft dike cu tting mafic flows, 3600 ft northeast of Facpi Poiti t.

Gm 1-2 Mafic boulder, from pyroclastic conglomerate east of Mount Alutom.

Gm 25-1 Mafic boulder, pyroclastic conglomerate east of Mount Tenjo.

Sampleno. DESCRIPTION OF SAMPLES

Go 6-1 Mafic boulder, pyroclastic conglomerate, Spruance Drive.

le 3-1 Mafic boulder, Dandan area.

Ie2-l Mafic boulder pyroclastic conglomerate, Martinez Pasture, Dandan

area.

Go 10-2 Mafic boulder, pyroclastic conglomerate, Spruance Drive. 

If 6-1 Mafic boulder, Dandan Area.

Ss 9-1 Quartz porphyry, southeast slope Mount Santa Rosa. 

Fm 2-1 Green water-laid t.iff, Tenjo peak. 

Gm 9-1 Brecciated silicified water-laid tuff, ridge southeast of road leading east

from Tenjo Road between Alutom and Tenjo Peaks. 

Gm 21-1 Green silicified water-laid tuff, Tenjo Road between Alutom and Tenjo

Peaks. 

Gm 33-1 Red and white clay altered from water-laid tuff, Tenjo Road between

Alutom and Tenjo Peaks. 

Gm5-la Water-laid tuff (relatively unaltered), Tenjo Road between Comar

Reservoir and Alutom turnofl.

Gm 5-lb Water-laid taff, green clay altered from Gm 5-la. 

Gm 5-lc Water-laid tuff, pink clay altered from Gm 5-lb.

RESULTS OP ANALYSES 

MECHANICAL COMPOSITION

The mechanical composition and pH of the soils on 

volcanic rocks and on limestones are given in table 3. 

The soils are generally clays or silty clays in recognition 

of which the textural term "clay" is used in the field 

descriptions. Table 3 shows that all the profiles of 

Atate clay contain similar amounts of clay «0.002

mm), although the percentages vary in different parts 

of the profile. Shallower profiles of the Guam clay on 

limestones also show less variation. The average 

percentages of grades of silt and clay in the Atate clay 

and Guam clay profiles are given below.

Atate clay Guam day

(7 profiles, 34 samples) (5 profiles, 8 samples)

Silt Clay Silt Clay

23. 5 70. 7 33. 0 58. 5
F8 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

TABLE 3. Mechanical composition, in percent, and pH of soils on volcanic rocks and on limestones 

[Analyst, P. D. Blackmon, U.S. Geological Survey; Tr., trace, <0.1 percent]

Desorijition Profile and

sample No.

Horizon DcpUi Pit Gravel

>2mm

Very

coarse

sand

1-2 mm

Coarse

sand

0.5-1

mm

Medium

sand

0.25-

0.5 mm

Fine

sand

0.10-

0.25 mm

Very

fine sand

0.05-

0.10mm

Silt

0.002-

0.05mm

Clay

<0.002

mm

Soils on volcanic rocks

ATATE CLAY

Red latosol on Alutom Formation.

Red latosol on Bolanos 

Pyroclastic Member of 

Umatac Formation.

Red latosol on Facpi Volcanic Member of Umatac 

Formation.

Red latosol on Alutom 

Formation.

AS AN CLAY

Brown regosol on Alutom 

Formation.

S54-4-1

4-2 

4-3 

4-4 

4-5

S54-5-1 

5-2 

5-3 

5-4 

5-5

S54-6-1 

6-2 

6-3

6-4 

6-5 

6-6

6-7

S54-10-1 

10-2 

10-3

S54-12-1 

12-2 

12-3

12-4

19-^

12-6

12-8

S54-20-1 

20-2

20-3

S54-21-1

21-2 21-3

21-4

S54-23-1

A

A 

B 

B 

C

A 

B 

B 

B 

C

A 

A 

B

B 

B 

C

C

A 

A 

B

A 

B 

B

C

C

C

C

A 

B

B-C

A

B 

C

C

A

0-6 in.

7-20 in. 

20-30 in. 

30-51 in. 

51-60 in.

0-6 in. 

6-18 in. 

18-53 in. 

53-60+ in. 

10. 0-10. 5 ft

0-2 in. 

2-10 in. 

10-16 in.

16-32 in. 

32-46 in. 

46-60 in.

13. 5-14. 5 ft

0-3 in. 

3-15 in.

15-28 in.

0-6 in. 

6-13 in. 

13-40 in.

40-84+ in.

9. 0-10. 0 ft

15. 0-16. 0 ft

22. 5-23. 0 ft

0-4 in. 

4-16 in.

16-36 in.

0-16 in.

16-36 in. 

36-66 in.

8. 0-9. 0 ft

0-8 in.

5. 5

5. 8 

6. 0 

5. 4 

5. 4

5. 6 

5. 1 

5. 3 

5. 2 

4.7

5. 1 

5. 1 

5. 1

5. 0 

4. 9 

4. 8

4. 8

5.6 

5. 1 

5. 1

5. 3 

5. 1 

5. 3

5. 4

5. 0

4. 8

5. 0

6. 8 

5.6

5. 5

5. 4

5. 8 

5. 6

5. 8

5. 6

Tr. 

Tr. 

0. 1 

. 5

4. 0 

1. 9 

2.0 

1.7 

3. 8

. 2

. 2

. 2 

. 4

. 1 

. 1

. 1

Tr.

Tr.

Tr.

. 3

0. 1

. 3 

. 4 

. 1 

. 3

2. 0 

1. 0 

1. 0 

1. 2 

2. 4

. 3 

. 3

. 1

Tr. 

Tr. 

. 1

. 1

Tr. 

Tr.

. 1 

. 2 

. 1

. 1

. 1

Tr.

. 1

Tr. 

Tr.

Tr.

Tr.

0.7

. 3

. 5 

. 2 

. 6

1. 9 

.7 

.7 

1. 6 

1.7

. 2 

. 3 

. 1

. 1 

. 1

Tr.

Tr.

. 2

. 2 

. 1

. 1 

. 3 

. 2

Tr.

Tr.

Tr.

. 1

Tr.

Tr.

. 1

. 1 

. 1

. 1

. 1

1. 5

. 3 

. 5 

. 3 

. 6

1. 6 

. 6 

. 9 

2. 4 

1.7

. 4 

. 6 

. 4

. 5 

. 3 

. 2

. 5

.8 

. 9 

. 9

. 3 

. 3 

. 2

. 1

. 4

Tr.

. 4

. 4 

. 1

. 1

. 3

. 2 

1. 2

. 9

. 3

4. 6

. 6 

. 6 

. 5 

1. 5

1. 4 

1. 1 

2. 0 

2. 0 

2. 1

1. 2 

1. 9 

1. 4

1. 5 

. 8 

1.7

6. 3

2. 3 

2.5 

2. 5

1. 6

. 8 

. 5

. 8

2. 7

. 5

3. 2

1. 3 

. 3

. 6

3. 0

.6 

8. 1

6. 9

2. 4

4. 2

. 7 

. 7 

. 5 

1. 9

1. 1 

. 8 

1. 5 

2. 8 

1. 4

1. 2 

1. 5

. 8

. 9 

. 8 

2. 1

4. 5

2. 1 

1. 9 

1.7

2. 5 

1. 5 

. 5

1. 2

2. 9

1. 3

3. 5

1. 1

. 5

1. 1

3. 0

. 8 

8. 6

8. 2

4. 2

32. 4

14. 3 

12. 3 

22. 6 

26. 0

9. 9 

12. 9 

14. 5 

25. 3 

19. 2

20. 9 

25. 6

11.7

24. 4 

27. 6 

33. 1

50. 0

30. 6 

16. 5 

22. 6

28. 6 

34. 3 

10. 2

19. 8

30. 9

37. 1

39. 8

13. 3 

20.3

20. 5

24. 2

13. 3 

23. 6

30. 2

31. 0

56.

83.

85. 

75. 

68.

78. 

81. 

77. 

63. 

67.

75. 

69. 

85.

72. 

70. 

62.

38.

63.

77. 

72. '<

66.

62. ( 

88.

78. (

63.

61.

53.

83.

78.

77.

69.

85. 

58.

53,

61.

Soils on limestone

GUAM CLAY

Limestone.

Red latosol on Mariana 

Limestone.

FOSSIL SOIL

Fossil red latosol ____ _ __

See footnote at end of table.

S54-16-1

S54-17-1 

17-2

S54-18-1

18-2

S54-19-1 

19-2

S54-24-1

A

A 

B

A

B

A 

B

0-60 in.

0-3 in.

3-24 in.

0-1 in.

1-15 in.

0-4 in. 

4-12 in.

(] )

6. 1

7.8 

7.9

7.4

7. 4

7.0

7.8

7.8

Tr.

. 1 

2. 0

2. 0

Tr.

Tr.

. 1 

. 4

2.6

Tr.

. 3

Tr.

. 1

. 1

. 1 

. 1

2. 3

0. 5

1. 0 

Tr.

. 3

. 2

. 3 

. 1

2. 4

2.7

5.2 

. 6

2.7

1. 5

5. 9 

. 4

2.7

5. 4

5. 1 

1. 5

3. 1

2.5

9. 0 

1. 6

2. 6

28. 8

34. 9 

35. 4

40. 6

28. 3

40. 1 

44. 0

12. 4

62.6

53. 5 

62. 5

53. 2

67. 4

44. 4 

51. 4

73. 0
MINERALOGY OF SELECTED SOILS F9

TABLE 3. Mechanical composition, in percent, and pH of soils on volcanic rocks and on limestones Continued 

[Analyst, P. D. Blackmon, U.S. Geological Survey; Tr., trace, <0.1 percent]

Description Profile and

sample No.

Horizon Depth pH Gravel

>2 mm

Very

coarse

sand

1-2 mm

Coarse

sand

0.5-1

mm

Medium

sand

0.25-

0.5 mm

Fine

sand

0.10-

0.25 mm

Very

fine sand

0.05-

0. 10 mm

Silt

0.002-

0.05 mm

Clay

<0.002

mm

Soils on limestone Continued

CHACHA CLAY

Brown silty clav on Agana

Argillaceous Member of

Mariana Limestone.

S54-1-1

1-2

1-3

1-4

A

B

B

B-C

0-6 in.

6-18 in.

18-32 in.

32-46 in.

6. 5

5. 5

6. 5

6. 9

1. 5

. 1

3. 4

1. 2

Tr.

Tr.

3.2

1. 1

Tr.

Tr.

1.5

. 4

Tr.

Tr.

0. 5

. 3

. 1

Tr.

0.7

. 3

. 1

Tr.

2. 3

1. 1

5. 6

6. 9

86. <

95. {

94.

93. (

Sample obtained from 3-ft vertical channel in middle of 6-ft soil exposure on roadside steep cutbank.

Within each profile of Atate clay there are variations in amounts of both silt and clay, but there does 

not seem to be any regularity in this variation: for 

example, in profile S54-4 the lowest percentage of silt 

is in the B horizon, as it is in profiles S54-5, S54-6, 

S54-10 and S54-12; but in S54-20 the surface soil 

contains the least silt and the most clay. For nearly 

all these profiles the least clay content is in the C horizon and the maximum in the B horizon, although some 

of the A horizons also have a low percentage of clay. 

The shallow Guam clay on limestone contains less 

clay in the surface soil than at depth. The two brown 

soils, the Asan clay on the Alutom Formation and the 

Chacha clay on Mariana Limestone, differ from the 

other soils in being regosols or lithosols and hence 

differ in stage of development. The Chacha clay 

has a very high clay content, averaging 92 percent, with 

consequent low silt content. The surface of this soil, 

however, is much lower in clay than the remainder of 

the profile, but it has more coarse sand than the average soils analyzed. The surface Asan clay on the 

volcanic rocks has a higher clay content than the average clay in the latosols (Atate clay) developed on the 

same kinds of rocks.

All the soils contain small percentages of the sand 

grades. Profile S54-5 is the only one to show an 

appreciable quantity (10.2 percent) of gravel and sand 

grades; the highest percentage is at the surface and 

at a depth of 10 feet in the C horizon. Most of the 

soils reach maximum coarseness in the fine sand 

(0.10 to 0.25 mm) and very fine sand (0.10 to 0.05 

mm) grades. Most profiles have a slightly greater 

percentage of sand at the surface and at the base of the 

profile in the C horizon where coarse material probably 

reflects the composition of the parent material. The 

weatherable nature of the underlying rocks is reflected 

in the quantities of the silt and clay grades.

SOIL REACTION

The pH of a 1:5 soil-water suspension for all the 

soils is given in table 3. The readings range from 4.7

at the base of profile S54-5 to 7.9 at the base of profile 

S54-17 on Mariana Limestone. All the profiles of 

Atate clay on the volcanic rocks have pH readings which 

average 5.3; the Guam clay profiles average 7.4. 

The Asan clay on volcanics has a pH of 5.6, but the 

brown soil on limestone, the Chacha clay, has an average pH of 6.3.

The lowest pH readings in the Atate clay profiles 

are in the dry upper parts of the C horizon, whereas 

the shallow Guam clay profiles show little variation in 

pH or an increase towards the underlying limestone.

CHEMICAL COMPOSITION

The major chemical constituents in 6 soil profiles of 

Atate clay, 5 soil profiles of Guam clay and 1 soil 

profile each of Asan clay and Chacha clay are given in 

table 4. The constituents of particular importance 

with regard to soil formation and mineralogy are 

silica, alumina, iron, and water.

ATATE CLAY ON VOLCANIC ROCKS

In each soil profile (table 4) the percent of SiO2 in 

the Atate clay is less in the surface soil than in the C 

horizon. In some profiles there is a gradual change 

in quantity, but in others there is one soil horizon that 

is noticeably Jess siliceous than the others. In profile 

S54-4, the 20- to 30-inch horizon has 27.8 percent, 

whereas the horizon immediately above it has 28. 2 

percent and the surface (0 to 6 in.), 36.6 percent SiO2 . 

In profile S54-5, the 53- to 60-inch horizon contains 

30.3 percent SiO2 , whereas the 18- to 53-inch horizon 

contains 33 percent. In profile S54-12, the 13- to 40- 

inch horizon contains 22.4 percent SiO2 , whereas the 

horizon above and that below it contain 29.1 and 28.7 

percent SiO2 , respectively.

In some profiles there is little variation in the amount 

of A12O3 ; in others there is a slight accumulation, generally in the horizon that is somewhat depleted in SiO2 .

The total Fe2O3 content of the soils is variable; some 

of the Fe2O3 is in the free state (table 5; discussion 

on p. Fl]). In general, there is an accumulation
F10 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

TABLE 4. Major chemical constituents, in percent, in samples of soil from 13 soil profiles on Guam 

[Analysts: P. L. D. Elmore, K. E. White, P. W. Scott. Total Fe as Fe2O3]

Description Profile and 

sample

Horizon Depth SiO2 A12 03 Fe2O3 MgO CaO Na2 0 K2 0 Ti02 P2 05 MnO H2 0 CO2 Total SiO2

Al2O3+Fe2Oj

Soils on volcanic rocks

ATATE CLAY

Bed latosol on Alutom

formation.

Red latosol on Bolanos

pyroclastic Member

of Umatac Formation.

Red latosol on Facpi

Volcanic Member of

Umatac Formation.

Red latosol on Alutom

Formation.

ASAN CLAY

Brown regosol on

Alutom Formation.

S54-4-1

4-2

4-3

4-4

4-5

4-6

4-7

S64-5-1

5-2

5-3

5-4

5-5

5-6

S54-6-1

6-2

6-3

6-4

6-5

6-6

6-7

S54-10-2

10-5

S54-12-1

12-2

12-3

12-4

12-5

12-8

S54-20-2

20-3

S54-23-1

23-2

A

A

B

B

C

C

C

A

B

B

B

C

C

A

A

B

B

B

C

C

A

C

A

B

B

C

C

C

B

B-C

A

C

0-6 In.

6-20 in.

20-30 in.

30-51 in.

51-60 in.

11. 0-11. 5 ft.

12. 5-13. 0 ft.

0-6 in.

6-18 in.

18-53 in.

53-60+ in.

10. 0-10. 5 ft.

28. 5-29. 0 ft.

0-2 in.

2-10 in.

10-16 in.

16-32 in.

32-46 in.

46-60 in.

13. 5-14. 5 ft.

3-15 in.

11. 3-12. 3 ft.

0-6 in.

6-13 in.

13-40 in.

40-84+ in.

9. 0-10. 0 ft.

22. 5-23. 0 ft.

4-16 in.

16-36 in.

0-8 in.

8-36 in.

36.6

28.2

27.8

30.4

29.8

39.1

40.6

27.7

32.0

33.0

30.3

31.0

46.3

35.0

35.6

35.7

37.6

38.2

40.0

40.8

36.5

40.0

28.4

29.1

22.4

28.7

34.8

34.2

40.4

41.5

43.7

46.4

25.2

29.8

30.0

29.6

29.6

29.3

26.7

27.2

31.5

31.9

31.8

31.8

18.7

23.0

25.7

27.2

27.6

27.2

26.2

26.8

27.8

27.2

27.2

29.6

32.2

31.1

28.4

28.8

26.8

26.6

17.2

16.6

14.6

19.1

20.1

19.3

19.4

13.2

14.0

15.3

15.4

15.2

16.9

16.5

8.7

12.8

15.5

14.6

13.2

12.6

11.8

11.2

16.2

12.3

18.1

18.8

21.5

20.4

18.2

18.2

8.8

8.9

10.0

10.1

1.0

1.8

1.0

.82

.82

.83

1.1

.39

.31

.42

.42

.48

2.8

1.0

.82

.74

.82

1.1

1.2

1.2

.54

.87

.94

.59

1.5

.60

.61

.81

1.4

1.4

3.6

3.8

0.26

.09

.10

.13

.16

.12

.15

.20

.12

.09

.14

.11

.15

.30

.14

.12

.09

.10

.12

.10

.12

.11

.17

.11

.06

.13

.07

.08

.52

.46

.42

.48

0.07

.03

.04

.04

.02

.03

.05

.06

.06

.08

.06

.04

.04

.02

.04

.05

.04

.06

.01

.03

.03

.04

.04

.03

.04

.02

.03

.04

.03

.04

.08

.06

0.16

.17

.15

.06

.06

.08

.20

.12

.08

.12

.19

.16

.28

.10

.11

.08

.07

.12

.12

.07

.09

.22

.14

.09

.17

.07

.09

.11

.10

.13

1.1

1.5

0.92

1.1

1.2

.92

.84

.77

.74

1.2

1.1

1.0

1.1

1.3

.64

.92

1.1

.92

.87

.88

.82

.78

1.4

1.1

.92

.96

1.2

.98

.87

.88

.76

.80

.83

.74

0.19

.12

.10

.09

.08

.06

.06

.12

.06

.07

.07

.08

.10

.20

.14

.13

.12

.10

.10

.10

.14

.12

.18

.15

.10

.08

.06

.08

.08

.06

.09

.06

0.36

1.2

.96

.08

.03

.10

.20

.24

.02

.10

.12

.02

.02

.18

.08

.05

.04

.06

.11

.12

.12

.16

.52

.32

1.5

.25

.10

.14

.02

.01

.07

.16

15.8

17.7

17.4

17.4

18.2

16.6

16.0

17.8

18.3

18.6

19.1

If. 8

21.6

17.5

18.0

18.7

18.9

19.4

19.2

18.4

16.2

16.8

17.8

18.2

19.0

16.9

16.0

16.1

18.4

18.6

18.1

19.1

0.14

.24

.14

.09

.08

<.05

<.05

<.05

<.05

.08

.08

.08

.06

<.05

<.05

<-05

<-05

<.05

<.05

<-05

<.05

<.05

.14

<.05

.18

<-05

<.05

<.05

<.05

<.05

<.05

<.05

"95

100

99

99

99

100

100

'90

99

101

100

100

99

191

197

99

99

100

100

100

99

99

195

"98

100

99

99

99

197

99

1_95

99

0.92

.57

.55

.62

.61

.92

1.0

.65

.68

.70

.62

.64

1.69

.98

.86

.85

.92

.96

1.05

1.07

.83

1.01

.63

.60

.42

.56

.75

.73

1.13

1.17

1.61

1.74

Soils on limestone

GUAM CLAY

Red latosol on Barrigada Limestone.

Red latosol on Mariana Limestone.

FOSSIL SOIL

Fossil red latosol ___

CHACHA CLAY

Brown silty clay on

Agana Argillaceous

Member of Mariana Limestone.

S54-16-1

S54-17-2

S54-18-1

18-2

18-3

S54-19-1

19-2

19-3

S54-24-1

S54-1-1

1-2

1-3

1-4

1-5

A

B

A

B

D*

A

B

D*

A

B

B

B-C

D*

0-60 in.

3-24 in.

0-1 in.

1-15 in.

15+ in.

(Min.

4-12 in.

12-20 in.

« .__-__ 

0-6 in.

6-18 in.

18-32 in.

32-46 in.

46-52 in.

1.2

1.1

.74

1.0

2.2

2.3

22.4

26.8

33.0

34.2

34,4

41.1

42.6

37.3

40.0

35.3

38.5

38.6

24.8

29.0

30.4

29.7

22.6

22.1

19.7

21.0

17.0

19.4

15.3

19.0

16.2

14.6

14.6

0.74

1.2

.23

.16

.45

.47

.50

.58

.08

.54

.66

.66

.71

.67

0.40

.31

.78

.41

54.0

1.0

2.0

54.5

.36

.62

.25

.21

.36

54.3

0.03

.03

.07

.06

.06

.06

.07

.06

.07

.08

.08

0.08

.09

.06

.07

. .12

.14

.04

.10

.08

.08

.10

2.2

2.2

2.0

2.0

1.8

1.8

1.0

.94

.84

.88

.82

2.2

1.3

.82

.68

2.5

2.4

.22

.89

.76

.60

.64

0.84

1.2

.47

.45

.48

.36

.04

.48

.09

.06

.06

25.4

24.6

24.4

26.4

23.0

21.3

20.4

18.4

18.4

18.4

18.5

0.19

.26

.20

.50

.24

2.4

.35

.12

.08

.09

.08

197

197

187

193

184

'91

99

»93

99

100

100

0.02

.02

.01

.01

.04

.04

.41

.61

.73

.76

.78

i Organic matter present in appreciable quantity. 

» D horizon is parent rock.

» Sample obtained from 3-ft vertical channel in middle of 6-ft soil exposure on roadside steep cutbank.
MINERALOGY OF SELECTED SOILS Fll

of Fe2O3 in the upper parts of the profiles; for example, 

profile S54-5 contains 8.7 percent in the C horizon 

and 15.3 percent Fe2O3 at the surface. Table 4 shows 

that Fe2O3 tends to accumulate in the B soil horizon.

The presence of organic matter in the surface soils 

makes the determination of total water difficult, and 

the resulting figure may be inaccurate. There is little 

variation in water content in the horizons in any one 

profile, the figure for H2O for all profiles averaging 

17.8 percent. The figures obtained range between 

16.5 and 19.0 percent H2O for profile averages.

The remaining oxides (table 4), MgO, CaO, Na2O, 

K2O, TiO2, P2OS, MnO, and CO2, can be regarded as the 

minor constituents of the soils. There is little variation in the percentage of most of these oxides in each 

profile, but TiO2 and MnO show an increase, generally 

in the B horizon.

ASAN CLAY ON VOLCANIC ROCKS

The chemical composition of the Asan clay, a brown 

regosol developed on volcanic rocks, differs markedly 

from that of the red latosols (Atate clay). Silica is 

about 10 percent higher, but A12O3 is about the same 

as the average figure for the Atate clay. Ferric iron 

is lower, but total water is about the same. The most 

striking difference is in the MgO and K2O contents, 

which average 3.7 percent MgO and 1.3 K2O in the 

Asan clay compared with an average of 0.88 percent 

MgO and 0.12 percent K2O in the Atate clay profiles.

GUAM CLAY ON LIMESTONES

As the Guam clay is a shallow soil, variations in 

chemical composition within the profile are not noticeable. The SiO2 content is very low, averaging 1.4 

percent compared with an average of 35.5 percent for 

the soils developed on volcanic rocks. The A12O3 

content of the Guam clay averages 42.5 percent as 

against 28 percent in the Atate clays. The ratio 

between SiO2 and A12O3 is reflected in the kinds of 

clay minerals found in these soils. The Fe 2O3 averages 

20 percent; so Al2O3 +Fe2O3 account for more than 

60 percent of the soil substance. Much of the Fe2O3 

is present as free iron oxide on the outside of other 

mineral grains. The total water is 24 percent, which, 

with the high A1 2O3 content and low percentage of SiO2 , 

results in the presence of gibbsite in these soils (section 

on silt and clay minerals, p. F18-F24.

Of the remaining oxides given in table 4, CaO and 

TiO2 deserve mention. In profile S54-19, 1 percent 

of CaO is present in the surface soil and 2 percent at 

depth, which is higher than for any other soil analyzed. 

The TiO2 averages 2 percent, which is about twice as 

much as occurs in the soils developed from volcanic 

rocks and suggests an accumulation of TiO2 during the 

formation of these soils on limestones.

FOSSIL RED LATOSOL

The fossil red latosol that has developed on limestone resembles in its SiO2 content the Chacha clay on 

limestone, but its content of A12O3 resembles that of 

the Atate clay. The content of Fe2O3 is approximately 

the same as the average for the Atate clay.

CHACHA CLAY ON LIMESTONE

The Chacha clay on limestone although classified as 

a silty clay, is actually a clay with less silt content than 

any of the other soils described. In chemical composition it resembles some of the Atate clay profiles. The 

SiO2 ranges from 34 percent in the C horizon to 27 

percent in the surface soil (average, 32.1 percent), 

and its distribution is similar to that in the Atate clay. 

The A12O3 content is variable (average, 28.5 percent) 

with about 5 percent less in the surface soil than at 

depth. The highest concentration of Fe 2O3 , 19 percent, 

is at the surface, whereas the lowest soil horizon contains 14.6 percent (average, 16.1 percent). There is 

little variation in the other constituents throughout 

the profile; total water is 18.4 percent for each part of 

the profile. The TiO2 content is similar to that in the 

Atate clay and shows very little concentration in any 

part of this profile.

CHEMICAL CHARACTERISTICS

Chemical differences between the soils developed 

on the volcanic rocks and those on the limestones 

are most marked in the Atate and Guam clays; 

although they are also apparent in the brown soils on 

these rocks, for which few samples are available for 

study. The principal differences are shown by the 

averages for the various soil types. These averages 

are perhaps more valid for the Atate clay than for the 

other soils because of the much larger number of 

samples. The average contents, in percent, for a 

number of chemical constituents in these soils follows.

Clay Number 

of samples

34

2

6

4

Si02

35.5

45.0

1.4

32.1

A12O3

27.9

16.9

42.5

28.5

Fe2 08

14.5

10.0

20.3

16.1

HS 0

17.8

18.6

24.2

18.4

Ti02

1.0

.78

2.0

.87

MnO

0.20

.11

.63

.17

P205

0.10

.07

1.6

.72

FREE IRON OXIDE

The uncombined, easily removed ferric oxide of soils 

is generally referred to as the free iron oxide. Mineralogically it is geothite, hematite, or indefinite noncrystalline iron oxide, which is principally associated with 

the clay mineral particles to which it is firmly attached. 

It is considered that 75 percent of the free iron oxide 

of a soil is in the clay fraction.

The free iron oxide determined for these soils is given 

in table 5.
F12 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

Within the individual profiles of the Atate clay there 

is a considerable variation in free iron oxide content,

and in general the samples from the C horizon contain

much less than those near the top of the profile. This

is to be expected because the iron in the unweathered

volcanic rocks is largely present as FeO in combination

with alumina and silica in pyroxenes. The average

free iron oxide in the Atate clay is 11.4 percent. The

profile averages are 12.0, 13.2, 9.2, 11.7, 14.1, 4.1, and

11.1 percent, respectively. The reason for the low figure for profile S54-20 (4.1 percent) is not apparent; but

this soil has a higher exchange capacity than most, and

most of the iron may be in combination in a clay mineral, for some possible mixed-layered halloysite-montmorillonite is present in this profile.

TABLE 5. Organic carbon, free iron oxide, and ion-exchange

capacity of soils on volcanic rocks and on limestones

[Analysts, Dorothy Carroll and H. C. Starkey; n.d., not determined]

Description

Profile

and 

sample

Horizon

Depth

Organic

carbon

( Vpci nprcent)

Free 

iron

oxide 

(percent)

Ion-exchange 

capacity milliequivalents

per 100

grams

Soils on volcanic rocks

ATATE CLAY

Red latosol on 

Alutom Formation.

Red latosol on

Bolanos Pyroclastic Member of

Umatac Formation.

Red latosol on 

Facpi Volcanic

Member of 

Umatac Formation.

Red latosol on

Alutom Formation.

ASAN CLAY

Brown regosol on 

Alutom Formation.

S54-4-1 

4-2

4-3

4-4

4-5 

4-6

4-7

S54-5-1 

5-2

5-3

5-4

5-5 

5-6

S54-6-1

6-2 

6-3

6-4 

6-5

6-6 

6-7

S54-10-1

10-2 10-3

10-4

10-5

S54-12-1 

12-2

12-3 

12-4

12-5 

12-6

12-7 

12-8

S54-20-1

20-2 

20-3

S54-21-1

21-2 

21-3

21-4

S54-23-1 

23-2

A 

A

B 

B

C 

C

C

A 

B

B 

B

C 

C

A

A 

B

B 

B

C 

C

A

A 

B

C

C

A 

B

B 

C

C 

C

C 

C

A

B B-C

A

B

C

C

A 

C

0-6 in. 

6-20 in.

20-30 in. 

30-51 in.

51-60 in. 

11. 0-11. 5 ft

12. 5-13. 0 ft

0-6 in. 

6-18 in.

18-53 in. 

53-60+ in.

10. 0-10. 5 ft 

28. 5-29. 0 ft

0-2 in.

2-10 in. 

10-16 in.

16-32 in. 

32-46 in.

46-60 in. 

13. 5-14. 5 ft

0-3 in.

3-15 in. 

15-28 in.

28-60+ in.

11. 3-12. 3 ft

0-6 in. 

6-13 in.

13-40 in. 

40-84+ in.

9. 0-10. 0 ft

22. 5-23. 0 ft

0-4 in.

4-16 in. 

16-36 in.

0-16 in.

16-36 in. 

36-66 in.

8. 0-9. 0 ft

0-8 in. 

8-36 in.

2.9

.7

n.d. 

n.d.

n.d. 

n.d.

n.d.

5.0 

1.1

n.d. 

n.d.

n.d. 

n.d.

4.3

1.8 

2.2

.6 

n.d.

n.d. 

n.d.

3.4

.5 

n.d.

n.d.

n.d.

2.7 

1.2

.3

.5

.1

n.d.

n.d. 

n.d.

1.1

n.d. 

.6

2.5

.5 

.1

.06

1.5 

2.0

10.8 

15.4

17.7 

12.7

10.8

7.4

9.5

13.2 

14.7

15.4 

'20.4

14.4 

1.5

12.7

8.4 

10.8

8.4 

10.8

6.6 

6.6

14.7

10.8 

12.7

13.2

7.4

10.8 

12.7

19.8 

19.8

15.4 

12. 7

7.' 4 

14.0

4.0

4.3 

4.0

13.2

15.4 

7.3

8.4

4.3

4.0

11.4 

3.9

4.8 

6.6

6.6 

6.6

9.6

10.2 

7.2

8.1 

8.0

7.8 

33.6

17.1

13.8 

35.1

16.5 

19.5

23.7 

23.4

15.0

11.1 

9.9

10.2

11.7

11.1 

6.3

3.0

5.7

7.8 

8.4

12.0 

16.0

32.0

31.2 

23.2

20.8

19.2 

27.2

26.4

38.4 

40.8

See footnote at end of table.

TABLE 5. Organic carbon, free iron oxide, and ion-exchange 

capacity of soils on volcanic rocks and on limestones Continued

Description

Profile

and 

sample

Horizon

Depth

Organic

carbon 

(percent)

Free 

iron

oxide 

(percent)

Ion-exchange 

capacity

milliequivalents 

per 100

grams

Soils on limestone

GUAM CLAY

Red latosol on 

Barrigada Limestone.

Red latosol on 

Mariana Limestone.

FOSSIL SOIL

Fossil red latosolCHACHA CLAY

Brown silty clay on

Agana Argillaceous Member of

Mariana Limestone.

S54-16-1

S54-17-1 

17-2

S54-18-1 

18-2

S54-19-1

19-2

S54-24-1

S54-1-1

1-2 

1-3

1-4

A

A 

B

A 

B

A

B

A

B 

B

B-C

0-60 in.

0-3 in. 

3-24 in.

0-1 in. 

1-15 in.

0-4 in.

4-12 in.

0-6 in.

6-18 in. 

18-32 in.

32-46 in.

.1

5.9 

.4

4.4 

2.5

3.9

2.0

.06

3.3

1.1 

n.d.

n.d.

14.0

17.7 

16.8

20. 4 

20.4

16.8

20.4

10 o

1O. £t

4.0

7.4 

4.0

8.4

4.5

35.2 

6.6

26.4 

17.6

36.4

11.6

6. 3

13.5

11.4 

11.4

15.0

i Percentage is high, probably because of organic matter.

The free iron oxide in the samples of Guam clay

ranges from 16.8 to 20.4 percent with an average of

18.07 percent if S54-16 is included, which is nearly

twice as high as the content of the Atate clay. All

the figures obtained, with one exception, were higher

than those for the Atate clay. The fossil red latosol

on the Mariana Limestone, S54-24, has a free iron

oxide content similar to those obtained for the Atate

clay. The regosols, Asan clay (S54-23) and Chacha

clay (S54-1), have low free iron oxide contents, the

former averaging 4.1 and the latter 5.9 percent. The

low figures are probably due to a shorter period of

formation for these soils, as their color is brown and

not red as in the latosols. The principal iron oxide

mineral in the Chacha clay is goethite (table 7).

ION-EXCHANGE CAPACITY

The cation-exchange capacity of these soils is given

in table 5. The figures obtained vary within each soil

profile and between the different profiles and are a

reflection of the kind of clay mineral present. The

most completely weathered soils have the most uniform figures for ion-exchange capacity. In general,

the figure for the surface soil is higher than for samples

obtained in other parts of the profile, and this is most

probably due to the organic matter present. Increase

of ion-exchange capacity in the C horizon of profile

S54-5 is due to variation in the type of clay mineral

present, for it has been found (table 7) that montmorillonite occurs in the weathered rock constituting the C
MINERALOGY OF SELECTED SOILS F13

horizon, whereas the clay mineral in the upper parts 

profile is halloysite.

In the Atate clay, the ion-exchange capacity varies. 

Averages for the profiles are 7.0, 8.2 (33.6 at base), 

21.4, 11.6, 8.8, 28.8, and 24 milliequivalents per 100 

grams. The relationship between clay minerals and 

ion-exchange capacity of the Atate clay is shown by 

considering tables 5 and 7.

The surface soils of the Guam clay have a high 

ion-exchange capacity which is due to their high content 

of organic matter. The average for soil material 

without organic matter is 5.8 milliequivalents per 100 

grams, which is consistent with their clay mineralogy.

The brown regosols, Asan clay and Chacha clay, on 

volcanic rocks and on limestone, respectively, differ 

considerably. The Asan clay has an average ionexchange capacity of 39 milliequivalents per 100 grams, 

which includes the exchange due to organic matter. 

The Chacha clay averages 12 milliequivalents per 

100 grams (also including organic matter). The ionexchange capacity reflects essential differences in the 

mineralogy of these soils.

ORGANIC MATTER

As a measure of the amount of organic matter present 

in the surface samples of these profiles the organic carbon was determined (table 5). The average for the 

upper 6 inches of all these soils is 3.4 percent organic 

carbon equivalent to approximately 5.8 percent organic 

matter. In the lower parts of the soil profiles organic 

matter is present in small quantities, but it was not 

determined for all profiles. An Atate clay profile S54- 

12 (table 5) has 0.1 percent at a depth of 10 feet, and 

another profile, S54-21, has a small quantity at 8 to 9 

feet in the C horizon. The quantity of organic matter 

is higher in the Guam clays than in the Atate clays, 

but in the latter it may be more closely associated with 

the clay minerals and therefore more difficult to determine. The organic matter in the surface soils has 

resulted in low totals for the chemical analyses (table 4).

MINERALOGICAL COMPOSITION

SAND FRACTIONS

The minerals identified in the sand fractions are listed 

in table 6. As the soils on volcanic rocks average 94 

percent silt and clay, and the soils on limestones average 

91 percent silt and clay (table 3), only a small quantity 

of material coarser than 50 microns is present in any 

sample. The scarcity of coarse grains in the volcanic 

rocks has reduced the occurrence of sand-sized minerals 

in the soils. The fine sand (0.25 to 0.10 mm) and the 

very fine sand (0.10 to 0.05 mm) fractions were separated in bromoform to obtain the heavy minerals.

The quantity of heavy residue in these sand fractions 

varies within each soil profile and from profile to profile;

677-184 O 63 3

this variation is apparently the end result of differences 

in parent material weathering under similar climatic 

conditions. Calculation of the amount of heavy residue in the whole soil shows that the maximum amount 

is 3.5 percent in profile S54-10-1 to 10-5, Atate clay on 

the Bolanos Pyroclastic Member of the Umatac Formation, but many soils contain only a trace «0.1 percent) 

of heavy minerals. The soils overlying the limestones 

have a heavy-mineral content similar to that of soils 

on the volcanic rocks. Some profiles, notably S54-4-1 

to 4-7, S54-5-1 to 5-6, and S54-10-1 to 10-5, have an 

enrichment in heavy minerals in the surface horizon, a 

feature that has been noted elsewhere in old soil profiles; 

that is, in soils which have remained in place and have 

been subjected to soil-forming processes without disturbance for long periods.

The minerals present in the heavy residues are, in 

order of abundance, magnetite, other opaque grains 

(indefinite iron oxides and ilmenite), augite, hypersthene, greenish-brown and brown amphiboles. Zircon, 

sphene, and rutile occur sporadically in very small 

quantities.

Magnetite. Table 6 shows that magnetite is the most 

abundant of the heavy minerals and that it commonly 

makes up about three-quarters by weight of the heavy 

residue. It occurs in small octahedra and in irregular 

grains. Magnetite seems to be resistant to weathering 

under the conditions in which these soils are forming, 

but some of the goethite and hematite occurring as red 

and brown opaque grains probably has been derived 

from magnetite. Magnetite is a constituent of many of 

the lavas and tuffs on Guam, and it is therefore a 

residual mineral in these soils. Magnetite has, however, often been found in bands or layers in the weathered rock material, which suggests that there has been 

movement of material and that any concentration of 

magnetite in a surface soil may not be derived from the 

rock now immediately beneath the soil.

Ilmenite. The black opaque less strongly magnetic 

grains in the residues are ilmenite. Many are irregular 

in shape, but others are well crystallized with tabular 

rhombohedral crystals generally lying on the base c 

(0001) and showing rhombohedral faces. The presence 

of titanium was confirmed spectroscopically. Ilmenite 

occurs in much smaller quantities than magnetite and, 

as it is relatively resistant to weathering, has become 

concentrated in the surface soils. Many crystals have 

sharp-edged faces and do not have leucoxenic alterations, but in parts of some profiles, notably in the 

weathered rock at the base of S54-12, many ilmenite 

grains show corrosion pits. Such pitting indicates 

removal of part of the ilmenite by solution. It is 

probable that some of the parent rocks contain ilmenite 

that is well crystallized, whereas in other rocks the
F14 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

TABLE 6. Heavy minerals (sp gr in the sand fractions (0.25-0.10 mm and 0.10-0.05 mm) of soils from Guam,

[H. R., heavy residue, including magnetite; Mag. Fr., strongly magnetic fraction in sand; Tr., trace, <0.1 percent; n.d., not determined; A, major constituent; ++, present

in large amounts; +, present]

Profile and 

sample Horizon Depth

0.25-0.10 mm

H. R. (percent)Mag. Fr. (percent)

0.10-0.05 mm

H. R. (percent)Mag. Fr. (percent)

Total in soil '

H. R. (percent)

Mag. Fr. (percent)

Minerals

Ilmenite

Opaque 

red, 

brown

Augite Hypersthene

Amphibole

Green Brown

Others

Atate clay

S54-4-1 _

4-2....

4-3 _

4-4 

4-5. 

4-6....

4-7 

S54-5-1- .

5-2 _

5-3 

5-4....

5-5 

5-6 

S54-6-1 __

6-2 

6-3....

6-4....

6-5 

6-6 

6-7 

S54-10-1...

10-2...

10-3 _

10-4 ...

10-5 

S54- 12-1...

12-2...

12-3 

12-4 ...

12-5 

12-7 ...

12-6 

12-8 

S54-20-1...

20-2...

20-3...

S54-21-1 

21-2...

21-3 

21-4...

A

A

B

B

C

C

C

A

B

B

B

C

C

A

A

B

B

B

C

C

A

A

B

C

C

A

B

B

C

C

C

C

C

A

B

B-C

A

B

C

C

0-6 in.

6-20 in.

20-30 in.

30-51 in.

51-60 in.

11. 0-11. 5ft

12. 5-13. 0 ft

0-6 in.

6-18 in.

18-53 in.

53-60+ in.

10. 0-10. 5 ft

28. 5-29. 0 ft

0-2 in.

2-10 in.

10-16 in.

16-32 in.

32-46 in.

46-60 in.

13. 5-14. 5 ft

0-3 in.

3-15 in.

15-28 in.

28-60+ in.

11. 3-12. 3 ft

0-6 in.

6-13 in.

13-40 in.

40-84+ in.

9. 0-10. 0 ft

13. 4-13. 9 ft

15. 0-16. 0 ft

22. 5-23. 0 ft

0-4 in.

4-16 in.

16-32 in.

0-16 in.

16-36 in.

36-66 in.

8. 0-9. 0 ft

11. 6

9. 2

10. 5

5. 5

3.8

23. 1

13. 5

3.4

. 3

. 2

. 5

Tr.

1. 1

23. 1

56. 4

12. 9

17.0

18.9

8. 9

9. 2

54. 6

53. 3

26. 3

37. 9

5. 8

.9

. 6

3. 1

3.0

3.2

2. 1

1.0

0.3

3. 1

Tr.

Tr.

. 6

. 1

. 1

.3

9. 2

4. 4

7.4

.9

. 3

19. 1

4.2

. 3

Tr.

. 1

. 2

Tr.

1.0

18. 8

30. 1

10.9

13. 5

14. 8

8. 1

8.2

46. 3

49. 5

20. 7

34. 1

5. 8

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

1. 5

Tr.

Tr.

Tr.

Tr.

. 1

38. 0

60. 8

25. 4

33. 3

16. 6

48. 3

31. 4

7.8

. 9

1. 1

1.7

. 7

7. 8

52. 6

37.0

32. 4

43. 4

57.9

56. 6

36. 0

70. 5

51. 6

36. 9

49. 0

15. 1

^ Q

17. 9

12. 1

8. 3

11.4

. 6

7.5

1. 1

2.7

. 6

. 8

g

1. 5

1. 3

2. 8

26. 4

17.4

7.9

8. 3

4. 1

45. 0

17. 6

. 4

Tr.

. 5

. 2

Tr.

6. 2

42. 8

32. 9

26. 7

37. 5

55. 2

51. 6

34. 9

61.3

49. 0

31. 3

42. 8

15. 1

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

1. 5

.3

.4

Tr.

Tr.

Tr.

2. 1

2.7

. 7

. 5

. 3

. 5

. 6

Tr.

Tr.

. 1

Tr.

1.3

2.2

. 6

.9

.9

1.3

2.5

3. 5

2.9

1. 6

. 1

.3

. 1

. 1

.4

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

. 1

. 2

1.9

. 2

. 2

Tr.

. 1

Tr.

Tr.

Tr.

Tr.

Tr.

1. 0

1. 5

. 5

. 8

. 8

1.2

2. 4

3. 0

2. 7

1. 3

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

A

A

A

A

+

+

+

+

+

A

A

A

A

A

A

A

+

+ +

+ +

A

+ +

+ +

+

+

+ +

A

+

+ +

+

+

+ +

+

+ +

A

+

+ +

+

A

+

+

+

+

A

A

A

A

A

+

+ +

+ +

+

+

+

A

A

A

+ +

A

A

A

A

+ +

+

A

+ +

A

A

+ +

A

+

+

+

+

+

A

A

A

+

A

+ +

+

+

+

+

+ +

+

+

+

+

+ +

+

+ +

+

A

+

+ +

A

+

+

+

+

+

+

A

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

Asan clay

S54-23-1...

23-2...

A

C

0-8 in.

8-36 in.

Q 1

. 5

9 7 10 1

5. 5

n

K

5.0

0.6 O K + +

+

+

+

A

+

+ + +

Guam clay

S54-16-1 2 ..

S54-17-1 ...

17-2 2 _

S54-18-1 ...

18-2...

S54-19-1 

19-2 

A

B

A

B

A

B

0-60 in.

0-3 in.

3-24 in.

0-1 in.

1-15 in.

0-4 in.

4-12 in.

n.d.

7. 0

n.d.

°.Q 1

35. 7

8.3

40.0

n.d.

°. ^

Tr.

ion

7. 1

Tr.

30.0

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

. 4

1 9

. 7

. 9

n.d.

o

.4

. 1

. 7

+

A

A

+

+

A

+

+

+

+ +

+ +

+

+

A

A

+

+

+

+

+ +

+

See footnotes at end of table.
MINERALOGY OF SELECTED SOILS F15

TABLE 6. Heavy minerals (sp gr >#.#) in the sand fractions (0.25-0.10 mm and 0.10-0.05 mm) of soils from Guam Continued

[H. R., heavy residue, including magnetite; Mag. Fr., strongly magnetic fraction in sand; Tr., trace, <0.1 percent; n.d., not determined; A, major constituent; ++, present

in large amounts; +, present

Profile and 

sample Horizon Depth

0.25-0.10 mm

H. R. (percent)

Mag. Fr. (percent)

0.10-0.05 mm

H. R. (percent)Mag. Fr. (percent)

Total in soil »

H. R. (percent)Mag. Fr. (percent)

Minerals

Ilmenite

Opaque 

red, 

brown

Augite Hypersthene

Amphibole

Green Brown

Others

Fossil soil

S54-24-1 _

sample.

4.7 3. 8 22. 7 18.2 2.0 1. 6 + A

Chacha clay

S54-1-1 __

l-2_

l-3___.

1-4 _ _

A

B

B

B-C

0-6 in.

6-18 in.

18-32 in.

32-46 in.

13.6

10.3

.2

9.0

1.0

. 5

Tr.

Tr.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

0.7

.2

Tr.

TV.

Tr.

Tr.

A

A

A

+

+

A

A

A

+

+

+

+

-t1 Total found in 0.25-0.10 and 0.10-0.05 mm grades recalculated for whole soil; 

the figure will be slightly less than the true amount present because of small quantities probably present in other sand grades and silt.

ilmenite was originally irregular in shape. It is the 

irregular grains, probably more poorly crystallized, that 

are strongly corroded and pitted.

Red and brown opaque grains. Red and brown 

opaque grains are commonly present in all the heavy 

residues (table 6) where they represent alteration of 

magnetite and ilmenite to hematite and goethite. 

Many have a core of a black opaque mineral. These 

opaque grains are not dissolved by 1 + 1 HC1 to any 

great extent. In some residues these opaque grains are 

more abundant than ilmenite.

Augite. Augite in the soil heavy residues is similar 

to that described from the insoluble residues of the 

limestones (Hathaway and Carroll, 1963), but in the 

soils many of the grains are very strongly corroded. 

Figure 4 shows fresh and corroded augite. The most 

strongly corroded grains occurred in the Asan clay on 

the Alutom Formation (S54-23).

Augite is the major ferromagnesian mineral in the 

andesites, dike rocks, and tuffs of Guam. It has been 

incorporated in the limestones; so it may be present in 

a residual soil developed from a limestone. It is noteworthy that augite, together with hypersthene and in 

places amphibole, is of more common occurrence in the 

surface soils than in the subsoils and weathered rocks. 

Mohr and Van Baren (1954, p. 215) describe accumulation in soils in Indonesia and explain it as due to a 

late fall of volcanic ash. The senior author, from 

experience with many residual soils, believes that 

accumulation of magnetite, ilmenite, zircon, tourmaline, and other resistant minerals is due to the age of the 

soil in its present position, unless it can be proved that 

such minerals have been added from another source. 

It has been observed on many occasions that initial 

weathering of ferromagnesian minerals produces clay

2 Sand fractions too small in quantity for bromoform separation.

minerals, whereas those slightly more resistant minerals 

will show etched surfaces and no chemical alteration. 

There is a stage in the corrosion of such grains at which 

the optical properties change and the mineral can no 

longer be considered the same as it was originally; at 

this stage the mineral will lose chemical elements by 

solution and will eventually disappear.

Hypersthene. The hypersthene, where it is present 

in these soil heavy residues, is also similar to the 

grains observed in the insoluble residues of limestones. 

Generally, hypersthene is subordinate to augite in 

quantity, but in S54-5 it is equal in amount to augite. 

Many hypersthene grains are in stout prismatic 

euhedra which have been very little modified by 

weathering, although some corrosion is noticeable. 

Hypersthene is less corroded than augite and appears 

to be more resistant to leaching. In the parent rocks 

hypersthene is generally less plentiful than augite; 

so equal amounts in a heavy residue would suggest 

differential removal of augite.

Amphibole. Only negligible amounts of amphibole, 

principally a brownish-green variety, were observed. 

The grains are fresh and noncorroded. Amphibole is 

not at all abundant in the volcanic rocks of Guam, 

although some of the limestones contain appreciable 

quantities (Hathaway and Carroll, 1963).

Of the remaining heavy minerals listed, zircon, 

sphene, and rutile are very scarce. Minor amounts of 

zircon were observed in samples S54-5-3 and 5-4, and 

S54-6-1 to 6-7, S54-18-1, and S54-20-2. The zircon 

is either euhedral or rounded; the rounding, however, 

is not considered to be the result of erosion and redeposition, but to be an inherent characteristic. Sphene was 

observed in samples S54-1-1, S54-5-2, S54-18-2, and 

S54-20-1. Rutile is even scarcer than sphene. It is
F16 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

A. Atate clay, 0 to 6 inches, on Alutom Formation. Surface soil from profile S54-4, 

dark-reddish-brown clay. Fraction plus 140 (0.25 to 0.10 mm) nonmagnetic 

X 35. Opaques, augite, hypersthene.

B. Atate clay, 0 to 6 inches, on Alutom Formation. Surface soil from profile S54-5 

dark-reddish-brown clay. Fraction plus 140 (0.25 to 0.10 mm) nonmagnetic 

X 35. Augite, hypersthene, opaques.

C. Atate clay, 28.5 to 29 feet, soft weathered tuff, Alutom Formation, profile S54-5, 

the parent material of this soil, mottled white with yellow and red clay. Fraction plus 140 (0.25 to 0.10 mm), nonmagnetic X 35. Opaques, augite, altered 

hornblende.

FIGURE 4. Heavy residues of
MINERALOGY OF SELECTED SOILS F17

D. Atate clay, 0 to 16 inches, on Alutom Formation. Surface soil from profile 

S54-21, dark-reddish-brown clay. Fraction plus 140 (0.25 to 0.10 mm), nonmagnetic X 35. Augite, hypersthene, opaques. Both augite and hypersthene are corroded.

E. Asan clay, 0 to 8 inches, on Alutom Formation. Surface soil from profile S54-23, 

dark-grayish-brown clay. Fraction plus 140 (0.25 to 0.10 mm), nonmagnetic 

X 35. Opaques, augite (strongly corroded).

F. Guam clay, 0 to 4 inches, on Mariana Limestone. Surface soil from profile 

S54-19, yeHowish-red-clay. Total heavy residue, nonmagnetic X 35. (All 

less than Q.25 mm.) Augite, hypersthene, opaques.

»

*W *"V- * *

il TV V. f *

A **!*

 A. * "t ' ^ ^-^

 ^ "A*.* 0"--^*'*/i .* i3--« *^ A *w *^c».*y- E *«* 1*1 " Jk " .,!» ? * jk, 'Jf- - " '

-^

 ' '" A ^

k w* Hp^^ *_ ^|

^ V»>1 .^fRlmflf

sand fractions of soils on Guam.

r*a."- - * .* ' v:/- J
F18 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

apparently not formed authigenically from the alteration of ilmenite, which itself is not very plentiful in 

these residues or in the volcanic rocks. Anatase was 

not seen under the microscope, although X-ray diffraction charts indicated its presence in samples S54-17 

and S54-19.

CLAY AND SILT FRACTIONS

The minerals identified by X-ray examination are 

listed in table 7. Estimates of the amounts of the

various minerals in the samples are derived from the 

relative intensities of the diffracted lines. Because in 

addition to quantity of a mineral, many factors, such 

as variations in degree of preferred orientation, difference in degree of crystallinity, and variations in isomorphous substitution, affect diffraction intensity, 

these estimates can give only a general indication of 

the relative amounts of the minerals present.

TABLE 7. Mineralogy of the clay and silt fractions of soils

[Estimated amounts given as parts in ten; Tr., trace, <0.1 part; where a question mark precedes or replaces an estimate of quantity the identification of the mineral is doubtful; where a question mark follows an estimate of quantity the identification is reasonably certain, but the estimated amount is doubtful]

A. ON VOLCANIC ROCKS

Description Profile 

and sample

Depth Fraction HaUoysite Goethite Hematite Magnetite Gibbsite Quartz Alphacristobalite

Atate clay

Red latosol on Alutom

Formation.

Red latosol on Bolanos

of Umatac Formation.

S54-4-1

4-2

4-3

4-4

4-5

4-6

4-7

S54-5-1

5-2

5-3

5-4

5-5

5-6

S54-6-1

6-2

6-3

6-4

6-5

6-6

6-7

S54-10-1

10-2

10-3

10-4

10-5

0-6 in

0-6 in

6-20 in

6-20 in

20-30 in

20-30 in

30-51 in

30-51 in

51-60 in

51-60 in

11. 0-11. 5 ft

11. 0-11. 5 ft

12. 5-13. 0 ft

12. 5-13. 0 ft

0-6 in

0-6 in

6-18 in

6-18 in

18-53 in

18-53 in

53-60+ in

53-60+ in

10. 0-10. 5 ft

10. 0-10. 5 ft

28. 5-29. 0 ft

28. 5-29. 0 ft

0-2 in

0-2 in

2-10 in

2-10 in

10-16 in

10-16 in

16-32 in

16-32 in

32-46 in

32-46 in

46-60 in

46-60 in

13. 5-14. 5 ft

13. 5-14. 5 ft

0-3 in

0-3 in

3-15 in

3-15 in

15-28 in

15-28 in

28-60+ in

28-60+ in

11. 3-12. 3 ft

11. 3-12. 3 ft

Clay _

Silt ___-

Clayl__-

Siltl___-

Clayi 

Silt 1 __

Clay __

Silt__ _

Clay_____

Silt. -

Clay___ -

Silt______

Clay __

Silt_ __

Clay___-

Silt___ ___

Clay _

Silt ___

Clay 

Silt ___

Clay __

Silt _

Clay_____

Silt_-___

Plflv 2

Silt 2-_-.

Clay -

Silt__ __

Clay __

Silt ___

Clay -

Silt_-__-

Clay _

Silt ___

Clay 3--.

Silt ___

Clay 3 __-

Silt____ 

Clay 3 

Silt__-__

Clay _ 

Silt__ _

Clay 

Silt _ ___

Clay 

Silt . _

Clay __

Silt _ 

Clay_ 

Silt_____.

6

5

6

4

6

4

5

4

5

3

7

6

7

6

5

3

6

4

6

3

6

4

5

3

Tr.

8

6

7

6

7

5

7

5

6

5

5

5

7

7

6

5

6

6

7

7

7

7

8

8

1

1

Tr.

Tr.

Tr.

Tr.

1

1

2

2

Tr.?

1

2

1?

2

1

3

2

2

1

1

Tr.

Tr.?

1?

2

1

2

1

2

1

1

Tr.

1

Tr.

1

Tr.

2

1

2

1

1

1

1

Tr.

1

1

2

2

2

2

2

2

1?

1?

1

2

2

2

1

3

Tr.

1

1

2

3

3

1

1

Tr.

1

Tr.

1

Tr.

Tr.

2

1

Tr.

1

Tr.

Tr.

1

1

1

1

1

1

1

1

1

1

Tr

Tr.

Tr.

Tr.

Tr.

1

1

?

Tr.

1

Tr.

?Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.?

1

Tr.

Tr.

3

3

?Tr.

1

Tr.

1

2

2

Tr.

Tr.

Tr.

Tr.

2

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

1

Tr.

1

1

1

Tr.

Tr.

Tr.

Tr.

1

1

Tr.

?Tr.

1

Tr.

Tr.

Tr.

Tr.

?Tr.

?Tr.

Tr.

See footnotes at end of table.
MINERALOGY OF SELECTED SOILS

TABLE 7. Mineralogy of (he clay and silt fractions of soils Continued

A. ON VOLCANIC ROCK Continued

F19

Description Profile 

and sample

Depth Fraction Halloysite Goethite Hematite Magnetite Qibbsite Quartz Alphacristobalite

Atate clay Continued

Volcanic Member

of Umatac FormaRed latosol on Alutom

S54-12-1

12-2

12-3

12-4

12-5

12-6

12-8

S54-20-1

20-2

20-3

S54-21-1

21-2

21-3

21-4

0-G in

0-6 in

6-13 in

6-13 in

13-40 in

13-40 in

40-84+ in

40-84+ in

9. 0-10. 0 ft

9. 0-10. 0 ft

15. 0-16. 0 ft

15. 0-16. 0 ft

22. 5-23. 0 ft

22. 5-23. 0 ft

0-4 in

0-4 in

4-16 in

4-16 in

16-36 in

16-36 in

0-16 in

0-16 in

16-36 in

16-36 in

36-66 in

36-66 in >

8. 0-9. 0 ft

8. 0-9. 0 ft

Clay 

Silt_____-

Clay 

sat __.

Clay 

sat 

Clay 

sat 

Clay 

sat 

Clay 

sat 

Clay 

sat 

Clay 4 -

Silt » 

Clay 4 _

sat« 

Clay 4 -

Silt 4 .--.

Clay 

sat 

Clay 

sat 

Clay 6 -__

Silt 4 - .

Clay 6 .

Silt *_.___

7

6

6

5

5

3

6

4

7

5

8

5

8

5

8

6

8

8

8

8

8

7

7

7

7?

7?

1

Tr.

1

1

Tr.

1

Tr.

Tr.

1

1

1

Tr.

1

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.?

1

1

2

2

3

3

2

3

1

Tr.

Tr.

2

2

Tr.

Tr.

Tr.

Tr.

1

1

1

2

1

Tr.

1

Tr.

Tr.

1

1

Tr.

Tr.

1

1

Tr.

1

1

Tr.

1

Tr.

1

Tr.

Tr.

1

2

Tr.

2

Tr.

Tr.

Tr.

Tr.

Tr.

1

?

Tr.

Tr.

Tr.

____ Tr.

Asan Clay

Brown regosol on S54-23-1 0-8 in Clay 2 __ _ _ _ _ _

Alutom Formation. 0-8 in Silt 2 ______- _ _ _ Tr.

B. ON LIMESTONES

Description Profile and Depth Fraction 

sample (inches)

Halloysite Goethite Hematite Gibbsite Boehmite Quartz

Guam clay

stone.

S54-16-1

S54-17-1

17 9

S54-18-1

18-2

S54-19-1

19-2

0-60

0-60

0-3

O_Q

3-24

3-24

0-1

0-1

1-15

i 1 ^

0-4

0-4

4-12

4-12

Clay 

Silt 

Clay 7 ------

sat 7 

Clay 7 __---

Silt 7 -__-_--

Clay 

sat 

Clay -.

sat 

Clay 7 _._ _

Silt 7 --------

Clav 7

Silt 7 ___ --------

2

2

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

Tr.

1

1

1

2

2

2

2

2

2

2

2

1

1

1

1

6

6

5

5

5

5

7

7

7

7

4

4

4

4

2

2

1

1

3

3

3

3

Fossil soil

Fossil red latosol 8 S54-24-1 Clay _

sat - 4

1

1

1

1

2

3

See footnotes at end of table.
F20 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS 

TABLE 7. Mineralogy of the silt and clay fractions of soils Continued

B. ON LIMESTONES Continued

Description Profile 

and sample

S54-1-1

1-2

1-3

1-4

Depth 

(Inches)

0-6

0-6

6-18

6-18

18-32

18-32

32-46

32-46

Fraction

Chacha clay

Clay____ _

Silt ?__ _________

Clay._________.

Silt____________

Clay_.__-_-_-_-

Silt____________

Clay---___-__-

Silt__--_ _

Halloysite

7

1

7

1

6

6

6

4

Goethite

2

1

2

2

2

2

2

2

Hematite

Tr.

Tr.

Tr.

Tr.

1

Gibbsite Boehmite Quartz

3

4

Tr.

Tr.

Tr.

1 Contains chromite.

2 Principal clay mineral is montmorillonite.

3 Contains a little montmorillonite.

4 Contains a little mixed-layer montmorillonlte-halloysite. 

6 Contains weddelite.

The most abundant minerals are halloysite, goethite, 

hematite, and gibbsite with lesser amounts of montmorillonite, magnetite, boehmite, quartz, and alphacristobalite. One or two samples contain traces of 

anatase, chromite, or weddelite 1 (a hydrated calcium 

oxalate). Material that is probably randomly mixed 

layered halloysite-montmorillonite occurs in at least two 

of the samples.

Although no particles of tubular" shape were observed 

in electron micrographs of two of the samples, the 

kaolinite-group mineral revealed by the X-ray diffraction patterns was identified as halloysite rather than 

kaolinite or "fire clay" mineral on the basis of the 

following criteria:

1. Broad diffuse 001 peaks near 7.5A.

2. Broad poorly resolved hk bands, particularly 

those in the region 2.3A to 2.5A, of greater intensity 

than the OOl peaks.

3. Failure of the 001 reflections to show distinctly 

higher intensity in oriented aggregates.

Halloysite occurs primarily in the soils developed on 

volcanic rocks, whereas gibbsite together with some 

boehmite is dominant in the soil developed on relatively 

pure limestone. This relationship is brought out by 

figure 5, which shows a weighted estimate of the amounts 

of these minerals in each profile. Profile S54-23 is 

omitted because it contained neither halloysite nor 

gibbsite and boehmite. The normative amounts of 

halloysite and gibbsite calculated from the average 

chemical composition for each profile are shown for 

comparison. Profile S54-21 is omitted because 

chemical analyses were not made.

Differential-thermal-analysis curves (fig. 6 and table 

8) made by George T. Faust, U.S. Geological Survey, 

lend support to the identification of halloysite in 

samples S54-24-1, S54-1-2, S54-4-2 and 4-5, in view

1 The samples containing weddelite were collected from pasture land; therefore, 

this mineral may be of animal origin.

6 Principal clay mineral is mixed-layer montxnorillonite-halloysite.

7 Contains anatase.

8 Sample obtained from a 3-ft vertical chanhel in middle of 6-ft soil exposure on 

roadside steep cutbank.

of the high slope ratio due to asymmetry of the endothermic peak near 600° C. According to Bramao and 

others (1952), a high slope ratio does not exclude 

kaolinite, but its presence in conjunction with the 

X-ray characteristics mentioned above strongly suggests 

halloysite. Interpretation of the various thermal peaks 

is given in table 8.

TABLE 8. Interpretation of thermal reactions shown by 

differential thermal analysis curves in figure 6.

Sample

S54-17-2___

18-2___

24-l___

1-2. __

4-2___

4-5-_

23-1. __

Temperature (°C)

140 

360

542

875

140 

362

471

144 

338

608

972

141 

324

344

597

945

151 

330

602

962

151 

314

377

604

961

160 

361

588 

868

922

Endothermic

Adsorbed water _ 

Gibbsite

Boehmite

Adsorbed water _

Adsorbed water.

Adsorbed water. 

Gibbsite

Halloysite

Adsorbed water. 

Gibbsite

Adsorbed water. 

Gibbsite? . ___ __

Goethite? _ ___

Halloysite.

Interlay er water ____ 

(montmorillonite)

M ontmorillonite _ _ 

_-_do_-_. __________

Exothermic

?.

Organic matter.

Do.

Do.

Do.

Organic matter.

Montmorillonite.

Montmorillonite was dominant in only two samples, 

both overlying volcanic rock. One of these (S54-23-1) 

was collected from a roadcut in the Asan clay, a sapro-
PERCENT

O> tk 

O O 

PERCENT 

§ £ 8 o 

§3

i o . 

g T W < 2 s 

ro O 5 

° 3 §52 

fl I-5' 

rn 5.« 

z

0

g

00DO

(0

5 v tf a 

WI S Bf 

1 If 
F22

S-54 17-2 

(C 813)

37.4

GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

875°

S-54 18-2 

(C 814)

S-54 24-1 

(C 816)

38.6°

S-54 1-2- 

(C 800)

S-54 4-2 - 

(C811)

S-54 4-5 

(C 812)

S-54 23-1 

(C 815)

160° 588°

FIGURE 6. Differential-thermal-analysis curves of the clay «2 n) fraction of soils developed on limestones and on volcanic rocks. The analyses were made by George T. 

Faust, U.S. Geological Survey, who also assisted in their interpretation. Numbers in parentheses are laboratory numbers. Sample S54 17-2, Guam clay, on Mariana 

Limestone, detrital fades. 3 to 24 inches. S54 18-2, Guam clay on Mariana Limestone, molluscan facies. 1 to 15 inches. S54 24-1, Fossil latosol on Alifan Limeston e. 

S541-2, Chacha clay on Agana Argillaceous Member of the Mariana Limestone. 6 to 18 inches. S54 4-2, Atate clay, on Alutom Formation. 7 to 20 inches. S54 4-5, 

Atate clay, on Alutom Formation. 51 to 60 inches. S54 23-1, Asan clay, on Alutom Formation. 0 to 8 inches.
MINERALOGY OF SELECTED SOILS F23

litic soil younger than the other soils sampled; the other 

(S54-5-6) sample collected at a depth of 29 feet is a 

highly weathered tuff from asmall mesita of Atate clay. 

As very little other than montmorillonite was revealed 

by X-ray examination, structural formulas were calculated from the chemical analyses (table 4) by the 

method of Marshall (1949, p. 58). Ferrous iron was not 

determined in these samples because of the presence of 

organic matter. Calculation of the formula for S54- 

5-6, assuming that all the iron is in the ferrous state,

was also made. It is probable that the true formula 

lies between these extremes near the ferric end, for the 

material occurs in an oxidized zone. In both calculations the sum of octahedrally coordinated cations indicates that the minerals are dioctahedral. This agrees 

with the X-ray diffraction data that show 060 spacings 

in the region of 1.50 A, characteristic of dioctahedral 

montmorillonites.

The structural formulas calculated for the three 

samples are given below.

S54-25-1, Asan clay, 0 to 8 inches

[(Al1 . uFe.+6SMg.43Ti.05Mn) (Si3 .51 A1.49 )010 (OH)2] (K.uNa.m Ca.o,)

2.22

S54-5-6, Atate clay, 28.5-29 feet

[Iron calculated as ferric iron]

[(Al1 .33Fe.+5?Mg.32Ti.04Mn)(Si3.61A1.39 )01 o(OH)2](K.o3NaCa.o1 )

2.20

S54-5-6, Atate clay, 28.5-29 feet

[Iron calculated as ferrous iron]

2.35

Goethite and hematite are present in most of the 

soils, and their variation in abundance is shown in 

figure 7. The normative amounts of these minerals 

were calculated from the chemical analyses, assuming 

the ratio of goethite to hematite suggested by the X-ray 

data. In weighting the estimated amounts from table 

7, estimates indicated as "trace" (Tr.) are arbitrarily 

assigned a value of 0.2 part in ten. The water in excess 

of that required for the formation of normative halloysite, gibbsite, boehmite, and goethite in these soils is 

also shown in figure 7.

Total water only was determined in the chemical 

analyses because of the interference of organic matter. 

The excess water shown in figure 3 therefore includes 

adsorbed water and water contained in the organic matter in the sample. In general, the excess water amounts 

to about 6 percent, except in profiles S54-24 and S54-16 

where it is about 2 percent. As both of these profiles 

contain practically negligible amounts of organic carbon 

(table 5) compared with, the other profiles, this lower 

amount of excess water is probably a reflection of low 

content of organic matter.

Profiles S54-20 and S54-19 show amounts of excess 

water somewhat higher than the average. As none of 

the samples in these profiles show excessive amounts of 

organic carbon (table 5), water contained in the organic 

matter of the samples is not responsible for the excess. 

It is significant in profile S54-20 that 9.5 percent excess

silica results in the calculation of its normative composition. As mixed layered halloysite-montmorillonite is 

present in this profile (table 7), the "excess" water and 

silica probably occur in montmorillonite layers randomly interstratified with halloysite. Comparison of 

the estimated and calculated amounts of halloysite 

shown in figure 2, together with the amounts of "excess" 

silica and water, suggests that 10 to 15 percent of the 

material estimated as halloysite is montmorillonite randomly interstratified with the remaining halloysite.

Profile S54-10, on the other hand, contains no excess 

silica, but underestimation of the amount of gibbsite 

relative to boehmite would be revealed as excess water 

in the calculation. It is therefore possible that the 

estimate for the amount of boehmite in profile S54-19 

is high by a factor of about 2. Kecalculation would 

then yield about 5.5 percent excess water, which would 

correspond more closely to the average "excess" water 

in the various profiles.

The only other substantial overestimate occurs in 

profile S54-5; the estimated goethite and hematite exceed the normative amounts of these minerals by a 

factor of about 2. In the rest of the profiles, the X-ray 

and chemical data are in good agreement when the limitations inherent in quantitative estimations by X-ray 

methods are considered.

Together, the two sets of data indicate that a high 

halloysite-low gibbsite content is usually associated
F24 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

20

10

H

GOETHITE

tl ^

 |

r^rn r^i i W 1

S-54-4 S-54-5 S-54-6 S-54-10 S-54-12 S-54-20 S-54-1 S-54-24 S-54-16 S-54-17 S-54-18 S-54-19

PROFILE NUMBERS

25

20

10

HEMATITE

S-54-4 S-54-5 S-54-6 S-54-10 S-54-12 S-54-20 S-54-1 S-54-24 S-54-16 S-54-17 S-54-18 S-54-19

PROFILE NUMBERS

15

10

EXCESS WATER

S-54-4 S-54-5 S-54-6 S-54-10 S-54-12 S-54-20 S-54-1 S-54-24 S-54-16 S-54-17 S-54-18 S-54-19

PROFILE NUMBERS

FIGURE 7. Diagram showing percentage of goethite and hematite in the various soil profiles and water in excess of that required to form normative halloysite, gibbsite, and 

goethite. Stippled columns represent weighted averages of amounts estimated from X-ray analyses. Open columns represent normative amounts calculated from the 

average chemical composition of each profile using the goethite : hematite ratio suggested by the X-ray data.

with soils developed on the volcanics, whereas high 

gibbsite-low halloysite soils are restricted to the nonargillaceous limestone areas. Two limestone soil profiles do, however, contain major amounts of halloysite. 

It may be significant that both of these occur in the 

outcrop area of the Agana argillaceous Member of the 

Mariana Limestone, which had been shown (Hathaway 

and Carroll, 1963) to contain a noncarbonate fraction 

resembling the volcanic soils in mineralogic composition.

SOIL GENESIS 

EVIDENCE FROM CHEMICAL COMPOSITION

The chemical composition of the soils shown in tables 

4 and 10 indicates that there is a striking difference in 

the latosols developed on the volcanic rocks (Atate clay) 

and those on the relatively pure limestones (Guam clay); 

the single profiles of supposedly younger soils, the Asan 

clay (on volcanic rocks) and the Chacha clay (on argillaceous limestone), show fewer differences.

Following the method of Hough and others (1941) in 

assessing the gains and losses of chemical constituents

in soil profiles developed on the basaltic rocks of the 

Hawaiian Islands, the chemical analyses of the presumed 

parent rocks (table 2) of the Guam soils on volcanics 

were averaged and then recalculated on a water-free 

basis with the results shown in table 9. Then the 

analyses of samples from the soil profiles were recalculated on a water-free basis, and a weighted average 

composition for each profile was calculated. The 

weighting was done by considering a section of the soil 

1 inch thick as a unit. Thus, an A horizon from 0 to 6 

inches thick is considered as 6 units. Table 4 shows 

that 4 of the profiles were sampled to a depth of 60 

inches; in addition, there are samples of highly weathered rocks that are considered representative of the 

C horizon. Table 10 gives the weighted average composition of 9 of the profiles on a water-free basis.

SOILS ON VOLCANIC PARENT ROCKS

Each profile for which there is adequate chemical 

information can now be compared with its presumed 

parent rock based on field descriptions and locality. 

Unfortunately, fresh rocks could not be collected be-
MINERALOGY OF SELECTED SOILS F25

TABLE 9. Average chemical composition of three groups of volcanic rocks that are parent materials of soils on Guam

[A, complete analysis; B, analysis recalculated on a water-free basis. Figures in 

parentheses are number of analyses averaged. Analyses of the rocks are given 

in table 6]

SiOj._ . -

AljOsFezOs-- -

FeO. ... .

MgO_. .........

CaO.... ...

Na8 0. -.. 

KaO_._ ... ..

H2 0±.... . .

Ti02 .. ........

C02 ----- 

PS 08 .. ........

MnO..........

Basalt (11)

A

51.76 

15.24 

3.73 

5.20 

7.05 

9.08 

2.32 

.65 

4.05

.65 

.07 

.14 

.15

B

54.09 

15.92 

3.90 

5.43 

7.36 

9.49 

2.42 

.68

.68 

.07 

.14 

.14

Dikes (10)

A

59.80 

15.55 

2.62 

3.72 

4.10 

7.09 

3.09 

1.13 

2.63 

.49 

.14 

.12 

.10

B

61.35 

15.95 

2.68 

3.81 

4.20 

7.27 

3.17 

1.16

.50 

.14 

.12 

.10

Tuffs (4)

A

71.34 

10.75 

1.37 

.25 

.93 

2.24 

1.15 

.92 

10.47

.26 

.007 

.05 

.02

B

78.83 

11.88 

1.51 

.27 

1.03 

2.47 

1.27 

1.01

.28 

.007 

.05 

.02

Average volcanic 

material

A

60.96 

13.84 

2.57 

3.05 

4.02 

6.13 

2.18 

.90 

5.71

.46 

.07 

.10 

.08

B

64.75 

14.58 

2.69 

3.17 

4.19 

6.41 

2.28 

.95

.48 

.07 

.10 

.08

neath the soil profiles as the weathering processes have 

penetrated to average depths of 50 feet. However,

comparison with the composition of average basalt, 

dike rock, or tuff will give some indication of the movement of constituents within the profile. In making 

these comparisons, it is assumed that silica and bases 

have been removed and that alumina, iron, and titania 

have accumulated.

Atate clay, profile S54~4- This profile, from 0 to 60 

inches, is on the volcanic conglomerate, tuff, and coarsegrained pyroclastic material of the Alutom Formation. 

The parent material is considered to be the tuffs of 

table 9. The relationship between the parent rock 

and the soil is shown in table 11.

The chemical composition of samples from the 

weathered rocks at the base of this profile, at a depth 

of 11 to 11.5 feet and 12.5 to 13 feet, were averaged 

and recalculated to a water-free basis and then compared with the part of the profile from 0 to 60 inches, 

as shown in table 11,

TABLE 10. Average chemical composition (water-free basis}, in percent, of soil profiles developed on volcanic rocks and on limestones

from Guam

Soil type

SiO2 ____ ----- ----- -_-_-__ --- -.-

AM),--- ---------------------------- ---

Fe2 O3 -. . -------------------------------

MgO..- -_-------___-_- -----

CaO. ____ _-____-___-___--__.-- 

Na2 O and K8O_____-___-_________-_ _._

TiO2 _ ___-_-_____.____.____--__---_

P.O.--- - -----------------------

MnO___- _._.._.___.._.._._._.__._.._-_

Profiles developed on volcanic rocks

S54-4 

(0-60 in)

S54-5 

(0-60 in)

S54-6 

(0-60 in)

S54-12 

(0-84 in)

Atate clay

36. 80 

36. 0 

23. 20 

1. 34 

. 16 

.48 

1.21 

. 13 

. 63

39. 63 

39. 13 

19. 16 

. 50 

. 13 

. 22 

1. 29 

. 08 

. 11

47. 26 

33. 45 

16. 46 

1.21 

. 13 

. 16 

1. 11 

. 14 

.08

32. 87 

38. 29 

25. 22 

1. 12 

. 12 

. 15 

1. 28 

. 11 

. 84

S54-23 

(0-36 in)

Asan clay

57. 87 

21. 13 

12. 73 

4. 73 

. 58 

1.74 

.90 

.07 

. 16

Profiles developed on limestone

S54-16 

(0-60 in)

S54-1S 

(0-15 la)

S54-19 

(0-12 in)

Guam clay

1. 68 

57.58 

31.67 

1. 03 

. 56 

. 14 

3.08 

3.08 

1. 18

1. 46 

61. 55 

31. 29 

. 24 

. 64 

. 16 

3.00 

1. 02 

. 66

3.47 

57. 34 

28. 54 

. 74 

2. 55 

. 29 

2. 76 

3. 72 

. 60

S54-1 

(0-46 in)

Chacha 

clay

41. 00 

36. 16 

19.37 

.81 

. 39 

. 18 

1. 05 

.85 

. 14

TABIE 11. Chemical composition, in percent, of parent rock and soil profile, Atate clay on Alutom Formation

[Profile S54-4]

SiO2 ._ --...-.. .

AljOa. ----------

Fe2 O3 . ------------

FeO____ ____._-._. _-_

MgO... .. ___-___--___

CaO... _...__-_-_-__-

Na2O_ _ _ _____

K2 O__ ..-_____-___.. -

TiO2 __ _-----_--_

MnO... _--______-_

Average tuff

(a)

78. 8 

11.8 

1.5 

. 3 

1.0 

2. 5 

1.3 

1.0 

. 3 

. 1

Presumed 

losses 

from (a)

(b)

0 

0

} " 

1.0 

2.5 

1. 3 

1. 0 

0 

0

Remainder 

in profile

(c)

78. 8 

11. 8

1.8

0 

0 

0 

0 

. 3 

. 1

Remainder 

recalculated 

to 100 percent

(d)

85. 0 

12.7

1. 9

0 

0 

0 

0 

. 3 

. 1

Whole profile 

weighted 

average

(e)

36. 8 

36. 0

23. 2

1. 3 

. 1

} «

1.2 

. 6

Difference 

(e-d)

(f)

-48. 2 

+ 23. 3

+ 21. 3

+ 1.3

+ .1

+ .5

+ .9

+ .5

Weathered 

average rock , 

11 to 13 feet

(g)

47. 6 

33.4

16. 2

1. 1 

. 1

. 2

. 9 

. 1

Difference

(e-g)

+ 10. 8 

-2. 6

-7.0

+ .2 

0

+ .3

+.3 

+ .5

(d-g)

-37. 4 

+ 20. 7

+ 14. 3

-1. 1 

-. 1

-. 2

-. 6 

0
F26 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

The principal differences are that the weathered 

rock contains nearly 11 percent more Si02 , 2.6 percent 

less A1 203 , and 7 percent less Fe 2 03 than the average 

for the whole soil from 0 to 60 inches, which suggests 

that the soil-forming processes are active at this depth 

and that the principal changes take place or are initiated in the weathered rock.

Atate clay, profile 854-5. This profile, from 0 to 60 

inches, is on the Alutom Formation, a bedded fine- to 

coarse-grained sandy tuff, weathered to a depth of 50 

feet or more.

Samples of highly weathered rocks were collected at 

depths of 10 to 10.5 feet and 28.5 to 29 feet. The 

analyses of these materials were recalculated to a waterfree basis and then compared with the soil from 0 to 60 

inches, as shown in table 12. The weathered rock at 

10 to 10.5 feet is practically identical in chemical composition with that of the weighted average soil from 0 

to 60 inches. Differences, however, are apparent between the weathered rock at 28.5 to 29 feet and that 

at 10 to 10.5 feet; there is a decrease of 19 percent in 

Si02 , an increase of 15 percent in A1203 , an increase of 

9 percent in Fe 203 , a decrease of 2.8 percent in MgO, 

and an increase of 0.7 percent in Ti02 . Na 20 and K2 0 

in the weathered rock at 10 to 10.5 feet are one-half the 

quantity present in the weathered rock at 28.5 to 29 

feet.

This profile, therefore, shows a reduction in Si02 , 

MgO, CaO, Na2O, and K2O, but increases in A1203 , 

Fe2O3 , and TiO2 . If the analysis of average tuff is 

compared with that of the saprolitic rook at 28.5 to 

29 feet, it is seen that SiO2 has decreased and that 

A12O3 and Fe2O3 have increased, pointing to the mobilization of SiO2 at a very early stage in rock weathering.

Atate clay, profile 854-6. This profile, from 0 to 60 

inches, is on the Bolanos Pyroclastic Member of the 

Umatac Formation, a fine- to coarse-grained tuff mostly 

weathered to a depth of 65 feet. Samples of weathered

rocks from 13.5 to 14.5 feet were collected for comparison with the soil. The chemical analysis of this 

material was recalculated to a water-free basis in table 

13. There is very little difference in chemical composition between the weathered rock at 13.5 feet and 

the weighted average for the soil from 0 to 60 inches.

Atate clay, profile S54-12. This profile, from 0 to 84 

inches, is on pillow basalt of the Facpi Volcanic Member of the Umatac Formation weathered to a depth of 

75 feet or more (table 14). Comparison of the chemical 

composition at 9 to 10 feet with that at 22.5 to 23 feet 

indicated that there are only negligible differences. 

The average composition of the weathered rock is different from that of the weighted average of the whole 

soil at 0 to 60 inches. This profile has lost only a small 

percentage of its Si02 between the weathered rock and 

the profile as a whole; there is a small increase in 

A1203 , Fe20a, and TiO2 .

Asan clay, profile 854-28. This profile, from 0 to 36 

inches, is on the massive lapilli pyroclastic material of 

the Alutom Formation. As no samples of weathered 

rock were collected below this profile, no comparison 

of weathered rock and average profile composition is 

made. This profile has A and C horizons only, and 

the 8- to 36-inch horizon is of weathered rock or 

saprolite (table 15) and therefore comparable with 

Atate clay sample S54-5 at 28.5 to 29 feet (table 12).

A consideration of the information in tables 11 

through 15 shows that the principal process in the 

formation of these soils is the removal of silica from the 

profile. This results in a relative accumulation of 

alumina and ferric iron. The volcanic rocks consist 

almost entirely of weatherable minerals that release 

silica readily. Some minerals, such as zeolites and 

volcanic glass of intermediate or mafic composition, 

alter rapidly to clay minerals of the montmorillonite 

group.

TABLE 12. Chemical composition, in percent, of parent rock and soil profile, Atate clay on Alutom Formation

[Profile S54-5]

SiOa _.._. ______________

A1 2 O3 _______________

Fe 2O3 _________________

FeO___________________

MgO_.___________

CaO._____________ ___

Na2O____________

K2O____________

TiO2 __ _______

Average 

tuff

(a)

78.8 

11. 8 

1. 5 

.3 

1. 0 

2. 5 

1. 3 

1. 0 

.3

Presumed 

losses 

from (a)

(b)

0 

0 } °

1. 0 

2. 5 

1. 3 

1. 0 

0

Kemainder 

in profile

(0

78. 8 

11. 8

1. 8

0 

0 

0 

0 

.3

Remainder 

recalculated 

to 100 

percent

(d)

85. 0 

12. 7

1. 9

0 

0 

0 

0 

. 3

Whole 

profile 

weighted 

average

(e)

39. 6 

39. 1

19. 1

. 5 

. 1

} '

1.3

Difference 

(e-d)

(f)

-45. 4 

+ 26. 4

+ 17. 2

+ .5 

+ . 1 

+ .2 

+ 1.0

Weathered rock

10 to 10.5 

feet

(g)

36. 9 

37.8

19. 6

. 6 

. 1

. 2 

1. 5

28.5 to 29 

feet

(h)

56. 0 

22. 6

10. 5

3.4 

. 2

. 4 

. 8

Difference

(g-h)

-19. 1 

+ 15. 2

+ 9.1 

-2. 8

-. 1

* £

+ .7

(d-g)

+ 48. 1 

+ 25. 1

-17. 7

-. 6 

_ ^

0

+ .2

(d-h)

+ 29. 0 

-9. 9

-8. 6

-3.4

___ 2

0 

-. 5
MINERALOGY OF SELECTED SOILS) F27

TABLE 13. Chemical composition, in percent, of parent rock and soil profile, Atate clay on Bolanos Pyroclastic Member of the Umatac

Formation

[Profile S54-6]

SiO,.._. .__._.__..____

A13 03

FejOs 

FeO.._. __._..___._.._

MgO__. _._-.____.___.

CaO_. ..__.___...____

Na20__ ______..__..__ .

K,0_.._. .._._____.___

Ti03 . ________________

Average tuff

(a)

78. 8 

11.8 

1. 5 

. 3 

1.0 

2. 5 

1.3

. 3

Presumed 

losses 

from (a)

0>)

0 

0

} «

1.0 

2.5 

1. 3

0

Remainder 

in profile

(C)

78. 8 

11. 8

1. 8

0 

0 

0

. 3

Remainder 

recalculated 

to 100 percent

(d)

85. 0 

12.7

1.9

0 

0 

0 

0 

. 3

Whole profile 

weighted 

average

(e)

47.2 

33. 4

16. 5

1.2 

. 1

} '

1. 1

Difference

(e-d)

-37. 8

+ 20. 7

+ 14. 6

+ 1.2

+ .1

+ . 1 

+ .8

Weathered 

rock 13.5 to 

14.5 feet

(f)

48. 1 

31. 6

13. 2

1. 4 

. 1

. 1 

.9

Difference

(e-f)

-0.9

+ 1.8

+ 3.3

-. 2 

0

0

+ .2

(d-f)

+ 36.9 

-18. 9

-11.3

-1.4 

-. 1

-. 1

-. 6

TABLE 14. Chemical composition, in percent, of parent rock and soil profile, Atate clay on pillow basalt of the Facpi Volcanic Member

of the Umatac Formation

[Profile S54-12]

SiO,._____.___________

A13 03

Fe303 -- _____________

FeO__ .____- -.-._.._.

MgO_--.-_ ___--..... .

CaO--_-.--.-_--._-_-

Na3 0... ______________

K3 0__._____. _________

Ti02 ___. _____________

PA---- 

MnO__ _______________

Average 

basalt

(a)

54. 1 

15.9 

3.9 

5.4 

7.3 

9.5 

2.4 

. 6 

.7 

. 1 

. 1

Presumed 

losses 

from (a)

(b)

0 

0

} » 

7.3 

9.5 

2.4 

. 6 

0 

. 1 

0

Remainder 

in profile

(c)

54. 1 

15. 9

9.9

0 

0 

0 

0 

.7 

0 

. 1

Remainder 

recalculated 

to 100 percent

(d)

67. 0 

19.7

12. 2

0 

0 

0 

0

. 8

. 1

Whole 

profile 

weighted 

average

(e)

32. 8 

38. 3

25. 2

1. 1 

. 1

} '

1. 3

. 8

Difference

(e)-(d)

-34.2

+ 18. 6

+ 13.0

+ 1.1

+ . 1

+ . 1

+ .5

+ .7

Weathered 

rock 9 to 10 

feet and 22.5 to 

23 feet

(f)

40. 1 

33. 0

21. 1

.8 

+ 0

. 1

1. 0

0

Difference

(e)-(f)

-7.3

+ 5. 3

+ 4. 1

+ .3

+ .1 

0 

+ .3

+ .8

(d)-(f)

+ 26.9 

-13.3

-8.9

-.8 

0

-. 1 

-. 2

+. 1

TABLE 15. Chemical composition, in percent, of parent tock and 

soil profile, Asan clay on Alutom Formation

[Profile S 54-23]

SiOi...... ..........

A12 O 3 .. ............

Fe2 03 - ----------

FeO................

MgO. ..............

CaO.. ............

NasO.--. ..........

K2O__ ...........

TiO2 --. ...... ......

PiOs .. .............

Average 

volcanic 

rock

(a)

14.6

2.7

3.2

4.2

6.4

2.3

.9

.5

.1

Presumed 

losses 

from (a)

(b)

0

0

} «

4.2

6.4

2.3

.9

0

0

Remainder in 

profile

(c)

64 7

14.6

6.2

0

0

0

0

.1

Remainder recalculated 

to 100

(d)

T\ 14

16 9

7.2

> ---

Whole 

profile 

weighted 

average

(e)

Cm O

21.1

12.7

4.3

.6

1.7

Difference

(e-d)

17 3

1.1 0

+5.5

1 A Q

+.6

+1.7

+ 0

SILICA REMOVAL

In the latosols (Atate clay) the weighted average soil 

shows a loss of 34 to 48 percent SiO2 from that in the 

presumed parent rock, when compared on a water-free 

basis. Table 4 and figure 8 show that there is a progressive loss of silica towards the top of the profiles, the

top containing the least silica. This is a gradual loss, 

which indicates that there is no sharp differentation into 

horizons such as have been described for some Australian 

laterites (Carroll and Woof, 1951). The field descriptions of the Guam soils made by Stensland (p. F43- 

F49 also indicate that there is little development of 

distinct horizons in these soils, although the weathered 

rock (C horizon) often is mottled red or yellow and 

white.

The profile of Asan clay, a brown regosol on saprolitic 

volcanic rocks (table 15), differs from profiles of the 

latosols in that is has lost only 17 percent of SiO2 during 

profile development, suggesting that this is a younger 

soil than the latosols.

ALUMINA ACCUMULATION

In the latosols, alumina accumulation ranges between 

18 and 26 percent more than that in the parent rocks 

and has an average of 22 percent. The accumulation 

starts in the highly weathered rocks with the removal 

of SiO2 ; for example, in table 11, there is an accumula-
F28 GEOLOGY AND HYDROLOGY OP GUAM, MARIANA ISLANDS

ATATE CLAY 

S-54-4

SOILS ON VOLCANIC ROCKS, GUAM 

0 20 40 60 80 100 PERCENT

0-60"

ATATE CLAY 

S-54-5

11-13'

TUFF

0-60"

10-10'6"

:#;#Kvvvl ...... v.v I * * r* TUFF

ATATE CLAY 

S-54-6 0-60"

ATATE CLAY f~ 

S-54-12 Li

0-84"

9-10'

ASAN CLAY 

S-54-23

BASALT

0-36"

VOLCANIC 

ROCK

20 40 60 80 100 PERCENT

Si02 A12 03 Fe2 03 Ti02 Others

FIGDEE 8. Chemical composition of four profiles of Atate clay and one profile of 

Asan clay on volcanic rocks. The analyses were recalculated to a water-free 

basis. The figures used are in tables 11 to 15 for the soils and in table 9 for the 

average composition of the tuffs and basalts. The diagrams represent average 

amounts of S102 ., A12 O3 , Fe2 O3, and TiO2 weighted for the thickness of the soil 

horizons analyzed. No fresh rocks were obtainable beneath these soils. The 

composition of the presumed parent rocks of the soils are the averages for the 

different kinds of rocks. The kind of parent rock that probably underlies the 

soil profiles is that indicated by field occurrence and the geologic map.

tion of 20 percent for samples at depths of 11 to 13 

feet, only differing by 2.6 percent from the alumina in 

the soil. Weathered rock between 28.5 and 29 feet 

(table 12) shows an accumulation of 10 percent A] 2O3 

more than that in the presumed parent rock. The 

A12O3 content in weathered rock at 10 to 10.5 feet is 

approximately the same as that in the soil profile. 

Figures for alumina for weathered rocks at about this 

depth in other profiles are of the same order of 

magnitude.

The accumulation of alumina in the Asan clay only 

amounts, to 4 percent, which is about one-fifth of that 

found in the latosol profiles.

FERRIC OXIDE

The parent rocks do not contain much iron. The 

average basalt has about 4 percent Fe2O3 and 5.5 

percent FeO; the average tuff has much less, with 1.5 

percent Fe2O3 and 0.3 percent FeO. The average for 

all the volcanic rocks for which analyses are available 

is 2.7 percent Fe2O3 and 3.2 percent FeO. Ferrous 

iron present in pyroxenes, amphiboles, and volcanic 

glass is changed in the early stages of rock weathering 

to ferric oxide, which may be hematite, goethite, or 

indefinite iron oxides that become intimately associated 

with the clay minerals. No figures for ferrous iron 

were obtained for the soil samples because of the 

presence of organic matter and the consequent inaccuracy imparted to the FeO determinations.

Ferric oxide has accumulated in all the profiles 

examined. The increase in Fe2O3 ranges from 13 to 

21 percent for the latosols (Atate clay), but is only 5.5 

percent in the Asan clay.

In the soil descriptions (p. F43-F49) there is 

mention of iron concretions, but these are insignificant 

when compared with the amount of ferric oxide held 

in intimate association with the clay and silt minerals. 

The size distribution of the soil material (table 3) 

shows that there is a small amount of coarse material 

which would include any of these small iron concretions. 

There is no conspicuous layer of iron concretions in 

these soils similar to those in fossil laterites in Australia 

(Prescott, 1931), where their presence is thought to 

indicate seasonal movements of the level of the ground 

water owing to periodic wet and dry seasons.

TITANIA

The average TiO2 content of these groups of volcanic 

rocks (table 9) is 0.46 percent (0.48 percent on a waterfree basis), whereas the average for the upper part of 

the soils on these rocks is 1.16 percent (water-free 

basis). This is an accumulation of TiO2 amounting 

to more than twice the content of the parent rocks 

in which titanium is present as a constituent of ilmenite, titaniferous magnetite, and possibly of the 

pyroxenes.
MINERALOGY OF SELECTED SOILS P29

The accumulation of TiO2 is a feature of weathering 

and soil formation in tropical climates that has been 

noted many times (Hough and others, 1941; Sherman 

and others, 1948). Bauxite and laterites generally 

show an accumulation of TiO2 , which must therefore 

be regarded as inert or an almost insoluble oxide at 

the pH values found in most soils. Alien (1948, 

p. 621) records an increase in TiO2 in bauxite developed 

from basalt in Oregon; Gordon and Tracey (1952, 

p. 26) record a similar accumulation in the Arkansas 

bauxite; and Mohr and Van Baren (1954, chap. 4) 

quote numerous analyses of parent rocks and the laterites derived therefrom in which there is also an accumulation of TiO2 .

The Atate clay profiles described herein have a 

greater TiO2 content than that found in the single 

profile of Asan clay, which suggests that the Asan 

clay is at a younger stage of profile development than 

the Atate clay.

WATER

The presence of water is essential for the formation 

of the clay minerals and of gibbsite. Table 4 gives the 

quantity of water in these soils. The average for the 

soils of volcanic parent material is 17.95 percent. 

This water can be used to calculate the normative clay 

minerals present in the soils in the same way as the 

normative mineral compositions of igneous rocks are 

calculated. The normative clay minerals are kaolinite or halloysite (2SiO2-Al2O3-2H2O) and gibbsite 

(A12O3 -3H2O), together with goethite (Fe2O3 -H2O) 

and (or) hematite (Fe2O3 ), and ilmenite (FeO-Ti02 ). 

Any silica not used for normative kaolinite or halloysite in these normative calculations is assigned to 

to normative quartz. The Guam soils, however, do not 

contain sufficient silica to form normative quartz.

The normative compositions of 1 Atate clay profile, 2 

Guam clay profiles, 1 fossil red latosol, and 1 Chacha 

clay profile are shown in table 16.

The dominant clay minerals identified by X-ray 

diffraction in the upper parts of these soils were halloysite in the soils developed from volcanic rocks and on 

argillaceous limestone, and gibbsite in the soils developed 

on relatively pure limestone. The origin of the clay 

minerals is discussed on pages F30-F36.

SOILS ON IJMESTONES

The soils on the limestones are very similar in 

appearance to those on the volcanic rocks, but they 

differ in chemical composition (tables 4, 10). The 

most conspicuous difference is the low silica content. 

The principal soil type is the red latosol known as 

Guam clay, but brown soils also occur in smaller areas. 

A profile of the latter type, Chacha clay, was also 

examined.

TABLE 16. Normative clay mineral composition, in percent, calculated from chemical analyses, of soil profiles on volcanic rocks and 

on limestones

[Ferric oxide calculated as geothite unless X-ray analyses showed only traces present. 

Low summations indicate that appreciable organic matter was in the samples. 

Sample S54-24-1 was obtained from 3-ft vertical channel in middle of 6-ft soil exposure on roadside steep cutbank. Sample S54-5-6 is predominately montmorillonite]

Sample Depth Halloysite

Gibbsite

GoethiteHematite

Excess 

H2O

All 

others

Total

Atate clay on Alutom formation

854-5-1... . 

5-2..... 

5-3.... 

5-4 .. 

5-5..... 

5-6....

0-6 in.....

6-18 in. 

18-53 in.... 

53-60+in 

10-10.5 ft. - 

28. 5-29 ft 

59.6 

68.9 

71.0 

65.1 

66.6

5.6 

6.5 

5.9 

9.4 

8.4

16.9 

17.1 

16.9 

18.8 

18.3

5.9 

4.7 

4.9 

4.9 

4.7

2.3 

1.8 

1.8 

2.2 

2.3

90 

99 

101 

100 

100

Chacha clay on Mariana limestone

S54-1-1 . 

1-2.... 

1-3.... 

1-4. ...

0-6 in..... 

6-18 in.. .. 

18-32 in... . 

32-46 in....

57.6 

71.0 

73.6 

73.8

3.1

1.4 

2.0

.8

21.1 

17.9 

16.2 

16.2

7.1 

6.4 

5.8 

6.3

3.8 

2.8 

2.7 

2.9

93 

99 

100 

100

Fossil red latosol

854-24-1 48.2 29.9 17.1 1.6 2.2 99

Guam clay on Mariana limestone

854-18-1 

18-2...

0-1 in..... 

1-15 in....

1.5 

2.1

56.1 

59.8

19.7 

21.0

4.7 

5.4

4.6 

4.3

87 

93

Guam clay on Mariana limestone

854-19-1 

19-2....

0-4 in..... 

4-12 in--..

4.9 

4.9

51.0 

56.0

17.0 

19.4

4.7 

1.2

6.7 

9.7

84 

91

The Guam clay is similar in appearance and mineralogical composition to the red earthy deposits that 

overlie limestones in the Mediterranean regions and 

elsewhere and are known as terra rossa. Limestone 

areas in which terra rossa develops are all characterized 

by rapid drainage through the rocks, but few rivers are 

present. Many Pacific islands that have a core of 

volcanic rocks surrounded by limestones also have red 

soils on the limestones. Volcanic ash may have been 

deposited on these limestones during their deposition, 

as is known to have occurred in the Mariana and other 

limestones on Guam. Such limestones are impure 

and, on weathering, leave residual deposits that are 

very different from those on islands composed of 

coralline material alone.

The average chemical composition of the Guam clay 

is SiO2 , 1.4; A12O3 , 39.13; Fe2O3, 20.30; TiO2 , 2.0; 

H2O, 24.18 percent. The analyses indicate normative 

gibbsite and a little halloysite, the percentages of 

which have been calculated and are given in table 16.

SILICA

The low figures for silica in all the analyses of these 

soils (table 4) suggest that, if silica were originally 

present in greater quantities, it has been removed 

during soil-forming processes in which leaching is a
F30 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

major factor. It was noted that silica was removed 

from the Atate clay on the volcanic rocks, but the 

process has not been nearly so active as in the Guam 

clay. Some insight into the process may be obtained 

by comparing the chemical composition of one profile 

of Chacha clay (S54-1, table 10) with those of the Guam 

clays. The Chacha clay is a brown soil developed on 

argillaceous Mariana Limestone. The Chacha clay has 

41 percent SiO2 (Guam clay, average 1.4 percent), 

36 percent A12O3 (Guam clay, average 39.1 percent), 

19 percent Fe2O3 (Guam clay, average 20.9 percent), 

1 percent TiO2 (Guam clay, average 2.0 percent). 

In chemical composition the Chacha clay more closely 

resembles the Asan clay and the Atate clays on volcanic 

rocks than it does the Guam clay. It may be presumed 

that the first soil formed on argillaceous limestones will 

be like the Chacha clay, and on this presumption the 

changes in chemical composition during the development of the Guam clay are shown in table 17.

Table 17 indicates that silica has been lost and that 

the other constituents have increased, pointing to the 

fact that although conditions were favorable for the 

removal of silica, they were not favorable for the removal of iron from the Guam clay.

TABLE 17. Changes in chemical composition, in percent, of the 

Guam clay (average), presuming that it developed from material 

similar to the Chacha clay

[Major constituents on a water-free basis]

SiO2 ______-__.____.

A1S 08 -. --._--_. _-

Fe 2O3 --------------

Ti02 __._. _._.._.___

Guam clay 

(average, 3)

2. 3

58. 8

30. 5

2. 9

Chacha clay 

(single analysis)

41. 0

36. 0

19. 0

1. 0

Gain or loss 

in Guam clay

-38. 7

+ 22. 8

+ 11. 5

_i_i q

ALUMINA

The alumina content of the Guam clays averages 

39 percent. If it is assumed that the clay material in 

these soils was originally similar to that in the Atate 

clay derived from volcanic rocks, then removal of 

silica would cause increase in the percentage of alumina 

from 28 percent (Atate clay) to 39 percent (Guam clay; 

average for all samples). Silica can be removed in the 

slightly alkaline environment of the limestone soils in 

which the average pH is 7.4. Silicate minerals in such 

an environment will become corroded if they are fairly 

resistant to alteration, but less stable minerals may be 

completely decomposed.

FERRIC OXIDE

The iron oxide in the Guam clay averages 20.9 

percent, which is higher than that in the Atate clay, 

15.8 percent. It is present largely as free iron oxide 

(table 5) and is closely associated with the clay minerals,

using this term in a wide sense to include the aluminous 

oxides, gibbsite and boehmite. In limestones that 

contain detrital soil material, such as the Agana 

Argillaceous Member of the Mariana Limestone, the 

iron oxide is already associated with the clay minerals, 

and on soil formation it remains in the same position. 

The chemical environment of weathering is such that 

iron oxide cannot be removed by leaching surface 

waters because the pH is too high.

In ferric oxide content the Guam clay is similar to 

the average low-silica bauxite developed above limestones in central Europe as described by De Weisse 

(1948). The ferric oxide in 128 samples of such bauxites 

averages 22.9 percent. The presence of free iron oxide 

in terra rossa soils has been shown to have a relationship to the porosity of these soils (Mclntyre, 1956, 

p. 305), and its presence may have an important 

bearing on the removal of silica by leaching, leading to 

accumulation of alumina and subsequent formation of 

gibbsite and boehmite.

TITANIA

The Guam clay contains approximately twice as 

much TiO2 as the Atate clay and Asan clay formed from 

volcanic rocks, and the content of these rocks is quite 

low (0.5 percent TiO2 ). Accumulation of TiO2 is a 

common feature of lateritic weathering, particularly in 

tropical soils as described for the Hawaiian Islands by 

Hough and others (1941) and more generally by Mohr 

and van Baren (1954). Titania, like alumina, is not 

readily removed from soils by leaching, so if SiO2 and 

bases are removed by soil-forming processes, titania 

automatically increases. Bauxites developed on limestones all show about 2 percent TiO2 , which is the average for the Guam clay. The form in which titania is 

present may be as ilmenite, anatase, or as indefinite 

hydrous titanium oxide (TiO2 -nH2O) associated with 

the clay minerals. The conditions for the recrystallization of the anatase-brookite-rutile group of minerals 

are not well understood, but anatase is the mineral 

which most commonly crystallizes authigenically.

PHOSPHATE

Some of the limestones contain apatite that replaces 

shell fragments (Schlanger, 1963). The Guam clay 

contains 1.65 percent P2O5 compared with 0.1 percent 

P2O5 in the Atate clay. The phosphate in the Guam 

clay can probably be best explained as a residual 

constituent of the limestones that is not removed by 

leaching at pH 7 and therefore accumulates in the soils.

EVIDENCE FROM MINER ALOGICAL COMPOSITION

SOILS ON VOLCANIC ROCKS

Chemical analyses of the various soils developed on 

the volcanic rocks indicate that silica is removed by
MINERALOGY OF SELECTED SOILS F31

the soil-forming processes and that alumina, ferric 

iron, and titania show a relative increase.

The parent rocks basalts, mafic dikes, and tuffs 

contain variable quantities of minerals that can be 

altered by weathering and soil-forming processes. 

These rocks vary in coarseness of grain size and in 

texture (figs. 1, 2). The total effect of weathering 

processes may be complete removal of a mineral, a 

reduction in the amount present, or a change of the

original mineral into clay minerals and iron oxides. 

Some of the minerals are resistant to weathering and 

persist in the resulting soil. The weatherability of a 

rock can be diagnosed from a consideration of the kinds 

of minerals present or from a chemical analysis. One 

way to estimate the weatherability is to use the Weathering Potential Index (WPI) as suggested by Reiche 

(1950). This is the mol percentage ratio of the sum 

of the alkalis and alkaline earths, less combined water, 

to the sum of the total mols exclusive of water; or

______ 1 00 X mols (K20+Na20+CaO+MgO-H20) __ 

Mols (Si02 + A1203 + Ti02+ Fe203 + FeO + CaO + MgO + Na20

___ 

K20)

This Weathering Potential Index is based on the observation that the order of loss of cations from rocks 

undergoing weathering appears to be Na, Ca, Mg, K, Si, 

Fe, Al, and Ti. This is probably true for the initial 

stages of weathering, but silica and ferric oxide accumulate with little loss under some conditions, although 

they are mobilized under others. In the normal process 

of lateritic soil formation Si02 is removed and Fe2 03 

accumulates. Alumina is the inert oxide under these 

conditions.

The Guam volcanic rocks include basaltic andesites, 

tuffs and coarser pyroclastics, and agglomerates. The 

principal minerals are plagioclase feldspars, pyroxenes 

(augite and hypersthene) with a little scattered olivine 

and quartz. Accessory minerals are magnetite, hornblende, biotite, and alkalic feldspar, together with glass 

in the matrix. The tuffs generally contain zeolites. 

All these, with the exception of quartz, are weatherable 

minerals so that, except for secondary silicification of 

some of the tuffs, the volcanic rocks contain only 

weatherable minerals.

The Weathering Potential Index of certain minerals 

is given by Reiche (1950) as follows: olivine, 54, 

augite, 39, hornblende, 36, biotite, 22, labradorite, 20. 

The WPI of the Guam volcanic rocks, using the average 

chemical composition of table 9, is 14, which suggests 

that the rock as a whole is not more weatherable than 

oligoclase. However, Reiche's WPI is too narrow a 

concept of weathering for soil formation studies where 

silica and iron oxides are also important.

The Weathering Potential Index of the weathered 

rocks beneath the soils, computed in the same manner, 

is nil, which indicates that no bases remain. This 

means that the initial weathering removes all the 

readily mobilized elements, and subsequent soilforming processes affect only the least readily removable 

elements, silicon, iron, and aluminum. The chemical 

analyses of the soils show this (table 4). In the agricultural use of these soils, deficiency of bases for plant 

nutrition would seem to constitute a problem. The

Minerals in rocks

Hypersthene ..

Hornblende... --.

Weathering potential index

17 

40 

30 

50

36 

22

50 

50

Cations removed

Ca,Na__._ 

Ca, Mg.. .......

Mg.Fe--- ..

Mg.FeCa, Mg, Fe, Na. 

K.Mg.Fe 

Ca.K.Na...... 

Mg.Fe.Ca.....

Minerals in 

weathered rocks

Montmorillonite ,' 

feldspar(?). 

Montmorillonite, 

augite. 

Hypersthene ......

Montmorillonite..

Hornblende," 

montmorillonite(?). 

Montmorillonite..

Montmorillonite. . 

 do.. 

Minerals in soil, 

final product

Halloysite.

Hallo ysite, 

augite. 

Halloysite, 

hypersthene. 

Halloysite. 

Magnetite. 

Ilmenite. 

Halloysite, 

hornblende.

Halloysite. 

Quartz. 

Halloysite. 

Do.

low pH and generally low figures for ion-exchange 

capacity also point to a deficiency of bases.

The minerals present in the rocks, weathered rocks, 

and soils are shown in table 18.

TABLE 18. Weathering sequence of minerals in rocks and soils of

Guam

1 In the presence of weathering pyroxenes, montmorillonite forms from plagioclase 

feldspar with magnesium being contributed by the pyroxene.

Examination of the sand-sized minerals (table 6) 

shows that magnetite is the dominant residual mineral 

in all the soils developed on volcanic rocks and that 

generally it is more abundant in the surface soil than 

in the deeper layers. The maximum quantity varies, 

the highest figure being 3 percent by weight of the soil. 

There are more than 4 ^ pounds of magnetite per cubic 

foot of surface soil of profile S54-10 (Atate clay). 

This fact, coupled with the depletion in Si02 and 

increase of A1203 and Fe203 (fig. 4), indicates that the 

increase in quantity of resistant minerals is the natural 

result of soil-forming processes that have been in 

operation for considerable periods of time. If augite, 

hypersthene, and hornblende are present, a similar 

accumulation is shown in spite of the fact that these 

are generally considered as weatherable minerals.

It is probable that in certain soil horizons alteration 

takes place more readily than in others, as suggested 

by Carroll (1953, p. 100); if a mineral survives alteration 

in such a zone, it may not again be subjected to con-
F32 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

ditions that would cause its removal. Furthermore, 

there are two ways in which minerals are affected by 

weathering processes; the mineral may be completely 

replaced by a clay mineral, for example, augite may be 

replaced by montmorillonite in a weathered rock which 

remains saturated with water; however, with free 

drainage, augite may retain its identity and optical 

properties although at the same time its substance is 

slowly removed by ionic solution. An indication of 

slow solution is the etching of grain surfaces shown in 

figure 4. It is commonly observed in deeply weathered 

rocks that zones or channels are developed through 

which water moves more readily than in other parts of 

the rock. Chemical elements are more easily removed 

from minerals adjacent to these channels than from 

those in other parts of the rock. The relatively undrained parts of a weathering rock are saturated with 

water containing chemical elements removed from the 

individual minerals present. This condition of the 

rock is conducive to the formation of alteration products 

of the original minerals. Clay minerals, sericite or 

other types of secondary mica, and crystallized titanium 

minerals, such as anatase or rutile, are commonly found. 

Examples of the early stages in the alteration of 

rocks of Guam are illustrated in figure 1C. Little loss 

of material has taken place, the principal change being 

the devitrification of glassy material and alteration to 

zeolites and montmorillonite. A more advanced stage 

is represented by figure ID. In figure 2A and B clay 

minerals are present in considerable abundance, but 

the mineral assemblage celadonite, saponite, and 

plagioclase suggests that intense weathering or leaching has not yet been effected. A highly weathered 

saprolite is represented by sample S54-5-6 (table 7) in 

which the earlier alteration products as well as the 

parent minerals have largely disappeared. The weathering process to this stage has been 

1. Transformation of unstable minerals to more stable 

phases without the loss of much material through 

leaching.

2. Development of dioctahedral montmorillonite as 

the dominant phase by the leaching of bases and 

silica from the earlier alteration products and 

remaining primary minerals. A feature of this 

stage is the retention of magnesium and loss of 

silica (table 12). The probable explanation is that 

little magnesium in excess of the amount necessary 

for the formation of montmorillonite is present in 

the parent rock, whereas the amounts of silica and 

alkalies exceed requirements and occur in glass or 

relatively easily soluble minerals. 

The Asan clay, represented by sample S54-23-1, has

reached this stage of weathering and soil development. 

Montmorillonite is replaced by halloysite (A1203 -

2SiO2 -2H2O), which may actually be endellite (A12O3 - 

2SiO2 -4H2O) within the soil and weathered rock. This 

transformation takes place in a random manner among 

the layers in montmorillonite, as shown by X-ray diffraction patterns indicative of a random interstratification of montmorillonite and halloysite layers. The 

lower horizons of profile S54-21 contain much interstratified montmorillonite and halloysite. Sampling 

was apparently not deep enough in the other profiles 

to show this transition, although small amounts of 

montmorillonite appear below 32 inches in profile S54-6. 

After this transformation of halloysite other changes 

take place only slowly, and all the profiles show a fairly 

uniform composition. One of the changes is the development of small amounts of gibbsite in the soils formed 

on the volcanic rocks. The normative amount does 

not exceed 7 percent in the profiles analyzed. The 

changes in mineral composition with soil development 

of these soils and some from other localities are summarized in graphical form in figure 9.

The vertical direction represents increasing degrees 

of soil development; the horizontal represents the composition of the soil at any given stage of development. 

The arrows indicate the transformations that the various minerals undergo. Nicolls and Tucker (1956, p. 

116) indicate that feldspar persists through the montmorillonite stage and then alters to halloysite. As no 

feldspar of significant quantity was noted in the montmorillonitic stage (Asan clay) of the soils of Guam, the 

location of the feldspar-montmorillonite boundary is 

doubtful. As the decomposition products of feldspar 

alone would be inadequate to form montmorillonite of 

the composition of the Asan clay, the contribution of 

magnesium from the ferromagnesians would be required. 

For this reason the ferromaganesian-montmorillonite 

and feldspar-montmorillonite boundaries are given approximately the same shape.

On figure 9 a dashed line is given as the boundary 

between montmorillonite and halloysite because of the 

presence of mixed layering between the two in the 

Guam soil, making the boundary gradational. The 

gradual transformation of goethite to hematite shown 

in the diagram is not evident in the Guam soils, but 

it occurs in some of the other localities shown. Because 

of such variations among the localities, no attempt is 

made to quantify the diagram; therefore a schematic 

relationship only is shown.

SOILS ON LIMESTONES

The limestones on Guam vary from almost pure 

calcium carbonate (table 1) to argillaceous limestones, 

and some contain phosphate. Magnesium carbonate 

is generally less than 3.0 percent in the samples 

analyzed. An examination of the insoluble residues,
MINERALOGY OF SELECTED SOILS F33

UJ

:>

Q.

o

_i

UJ 

UJ

O

Glass Zeolites 

BASALTIC LAVAS AND TUFFS

COMPOSITION Composition ranges of soils 

from various localities

FIGUEE 9. Diagram modified after Nicolls and Tucker (1956, p. 116) showing the mineralogical relation of soils developed on basaltic materials in various 

localities. Upward progression in the diagram indicates increasing degree soil development. Horizontal lines drawn across the diagram at various levels 

would indicate the composition of individual samples.

as reported by Hathaway and Carroll (1963), has 

shown that volcanic ash and argillaceous materials, 

derived from soils by erosion, have been added to the 

limestones during deposition. The volcanic ash contributed plagioclase feldspar, pyroxenes and amphiboles, magnetite, zeolites, and a little quartz; the eroded 

soil material contributed clay minerals and iron oxides, 

largely goethite.

The amount of material removed from limestones by 

solution by drainage waters depends on the purity

of the limestones; in pure limestones the weathering 

potential index is 100, but with increase in insoluble 

residues this figure decreases. The quantity of insoluble residue in the Mariana Limestone varies as shown 

in table 1, but as explained on page F2, these 

samples may not be representative. However, it is 

probable that the average insoluble content in the 

Mariana and Barrigada Limestones is about 0.1 percent. 

The insoluble residue of the Alif an Limestone averages 

about 4 percent by weight. The other limestones
F34 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

listed in table 1 are not parent materials of soils of 

significant area. The amount of insoluble residues in 

the limestones examined shows considerable variation.

The insoluble residues of some Guam limestones 

contain variable quantities of silica in four forms:(l) 

as a constituent of halloysite, (2) as beta-cristobalite, 

(3) as a constituent of zeolites, and (4) as a constituent 

of montmorillonite. In addition there are scattered 

small euhedral quartz crystals. Minor quantities of 

silica are present in augite, hypersthene, and hornblende. Ferric oxide is also a constituent of these 

limestones. It is closely associated with halloysite 

where it forms a coating on individual mineral platelets. This iron oxide has been carried into the deposition area as part of the eroded soil material, as explained 

by Hathaway and Carroll (1963).

The Guam clay associated with the Mariana Limestone is characterized by a very low silica content 

(average, 1.4 percent) and by high alumina and ferric 

oxide. The minerals in the insoluble residues of the 

limestones have been recognized in the sand, silt, and 

clay grades of the soils. In the sands (table 6) these 

minerals account for a maximum of 1.2 percent by 

weight (profile S54-18). Generally the quantity is less 

than 1 percent. In some of the soils examined there 

are practically no residual minerals that could be 

related to minerals of a weathered rather than to a 

fresh volcanic-ash assemblage. The least weatherable 

minerals in the soils associated with limestones are 

indistinguishable from those developed on the volcanic 

rocks, although the quantities of such minerals are 

generally smaller. Where present, magnetite is the 

dominant mineral, but ilmenite, augite, hypersthene, 

and amphiboles are also present. In addition to the 

individual heavy minerals, composite grains of augite 

and feldspar also occur in these soils. Feldspar and 

quartz grains are present in some of the sand grades.

Gibbsite is the most abundant mineral in the Guam 

clay associated with the Mariana and Barrigada 

Limestones. Some boehmite is present in two of the 

profiles and minor quantities of other minerals occur. 

Only minor amounts of gibbsite and boehmite occur 

either in the soils on volcanic rocks or in the insoluble 

residues of limestones. It seems apparent that gibbsite 

is formed by alteration of minerals, largely though not 

entirely clay minerals, in the chemical environment of 

limestone weathering. The process is one of leaching 

by solutions formed principally from rainwater, but 

which also contain organic acids and compounds. The 

minerals that are leached may be present as impurities 

in the limestones, or they may have been added to the 

limestone surfaces from outside sources. The deposit 

that results is known as terra rossa; in places it is

associated with hard limestones that have good 

drainage.

Small quantities of silica (<6 ppm) are soluble in 

water at all pH values (Correns, 1949, p. 210; 

Krauskopf, 1956, p. 1). Amorphous silica is many 

times more soluble than crystalline silica (100-140 

ppm). Silica is more soluble at higher than at lower 

pH values. Alumina is soluble below pH 4 and above 

pH 8; between pH 4 and pH 8 it is insoluble and is not 

present in soil solutions (Magistad, 1925, p. 193). 

Silica is therefore removed preferentially to alumina 

between these pH values, that is, at the usual pH values 

for soils. Leaching by solutions within these values 

will remove silica from easily weatherable minerals. 

If sufficient SiO2 is removed from clay minerals, their 

structure may break down and release A12O3 that can 

crystallize as gibbsite or boehmite. All clay minerals, 

however, do not alter in such a way that silica is added 

to the soil solution (Siever, 1957, p. 828). The change 

from a montmorillonite to a micaceous clay mineral does 

not involve a reduction in the amount of silica present.

The pH of the soils (table 3) show that this is the 

important factor in the decomposition of halloysite to 

gibbsite. Most of the soils developed on the volcanic 

rocks fall in the range of pH 4.8 to 5.8, in which silica 

goes into solution and alumina accumulates. The 

amount of silica removed depends on the quantity of 

rainwater percolating through the soil and saprolitic 

rock. The better the drainage the greater the possibilities for removal of SiO2 . The soils associated with 

limestones have pH values that range from 6.1 to 7.9. 

At these values silica is dissolved more readily than at pH 

4.8 to 5.8, but the soils are not sufficiently alkaline to 

remove A12O3 . The Chacha clay (profile S54-1) developed on the Agana Argillaceous Member of the 

Mariana Limestone illustrates the effect of quantity of 

material to be leached. The insoluble residue of the 

Agana Member consists of halloysite and goethite and 

a trace of gibbsite. The soil contains a maximum of 

3 percent gibbsite, whereas the Guam clay contains 

between 50 and 60 percent gibbsite (table 16).

That pH is not the only factor is illustrated by a soil 

collected from a small depression on the limestone ridge 

of Mount Lamlam that forms the highest point on the 

present-day island. X-ray examination by the methods 

described above shows that this soil contains principally 

montmorillonite and minor amounts of goethite and, in 

the upper 16 inches, minor amounts of gibbsite and 

boehmite. The horizons below 16 inches contain major 

amounts of silt-sized calcite.

The soil at Mount Lamlam is developed on Alifan 

Limestone which contains a considerable amount of 

montmorillonite, although it also contains an erosional 

or weathered assemblage of nonclay minerals (Hatha-
MINERALOGY OF SELECTED SOILS F35

way and Carroll, 1963). The presence of considerable 

silt-sized calcite in the lower horizons suggests a poorly 

drained relatively unleached soil. This lack of leaching 

accounts for the persistence of montmorillonite in the 

soil. The occurrence of gibbsite and boehmite in small 

amounts in the upper horizons suggests a development 

toward a high-alumina mineral composition without the 

intermediate formation of halloysite. This would suggest that a highly gibbsitic soil, such as the Guam clay, 

could form directly from a montmorillonitic noncarbonate residue in the limestone, if the drainage were 

good enough to provide strong leaching and the pH 

remains below 8. The Mariana Limestone on which 

the Guam clay most commonly occurs is for the most 

part highly porous and permeable and thereby provides 

very good internal drainage for the overlying soil. This 

limestone also has only a small insoluble content, and 

therefore it does not present at the weathering limestone surface a thick mass of residual clay particles 

which could retard drainage during the soil-forming 

period. Gibbsite cannot form in the presence of a 

sufficiently high concentration of silica in solution in 

soil water or in ground water.

As the Mariana Limestone contains an insoluble residue having both weathered and volcanic-ash mineral 

assemblages (Hathaway and Carroll, 1963), it is likely 

that the origin of at least part, if not most, of the Guam 

clay is the almost complete desilication of volcanic ash 

released from the limestone by solution and weathered 

under conditions of strong leaching and relatively high 

pH. The Chacha clay developed on the more highly 

argillaceous limestones, such as the Agana Member, 

which contain an erosional or weathered assemblage, 

tend to maintain a lower pH. This soil is subjected to 

less effective leaching, owing either to an abundance of 

clay that forms a relatively impervious blanket on 

release from the limestone or to the density of the underlying limestone. As a result, removal of silica takes 

place more slowly and the soil formed resembles the 

highly halloysitic Asan-type clay that was incorporated 

in the Agana during deposition.

On the question of the source of the insoluble content of the Alifan Limestone, the presence of iron oxides 

and nordstrandite and the absence of feldspars or 

zeolites (Hathaway and Carroll, 1963) suggest that a 

soil of the composition of the Asan clay, highly montmorillonitic, but a weathered soil material and not 

volcanic ash, was the contributing source. The montmorillonite could have been eroded from the volcanic 

areas in the early stages of weathering, during which 

montmorillonite was the dominant alteration product; or 

it could have been eroded after much longer weathering 

but from an area previously stripped by erosion of its 

halloysitic upper horizons.

Although means have been discussed whereby the 

noncarbonate minerals of the Mariana Limestone could 

alter to form the Guam clay, it is of course possible 

that this soil could have formed from materials derived 

from sources other than the underlying limestone. 

Zans (1952) proposed an alluvial origin for the Jamaican 

bauxites, suggesting that the material is eroded from 

soils on the volcanic areas of Jamaica and carried by 

the numerous streams draining these areas onto the 

limestones. This material may be deposited directly 

on the limestones or carried into solution channels or 

caves in the limestones. It may later be deposited on 

the floors of sinks and depressions if the water emerges 

as "boiling" springs.

The present topography of Guam is such that it is 

doubtful that any material from the volcanic parts of 

the island could reach the northern limestone plateau 

by river drainage. Any drainage to the north is intercepted by the Pago and Agana Rivers and carried to 

the eastern and western shores, respectively, close to 

the boundary between the volcanic rocks and limestone. 

Drainage from the limestone areas near this boundary 

is toward these rivers and away from the central parts 

of the limestone plateau. However, in the past, the 

limestone plateau was below sea level, and volcanic-rock 

weathering products undoubtedly were moved toward 

it.

The possibility that the limestone soils represent 

volcanic ash that fell on the limestone surface after its 

emergence must be considered. Such falls must have 

occurred even after the cessation of volcanic activity 

on Guam itself in Miocene time because of the presence 

of volcanic mineral assemblages in the Barrigada and 

Mariana Limestones. These ash falls must have originated from volcanic activity in places other than the 

present island of Guam. If the ash falls occurred after 

the emergence of the present limestones and during the 

present period of soil formation, evidence of the falls 

might be expected on the volcanic parts of the island 

in the form of repetitions of profile development. In 

particular, the more weatherable minerals should show 

sudden increases near the surface; however, such increases were not found in the soils developed on the 

volcanic areas.

It is also possible that windblown soil material from 

the volcanic soils was deposited on the limestone surface 

of the northern plateau. This soil material would 

become incorporated into the weathering products of 

the limestones. The prevailing winds of today are the 

Northeast trade winds. Soil material transported by 

them would be largely moved away from the island and 

deposited in the ocean. However, it has been noted 

that soil material is moved by breezes and winds from
F36 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

other directions, and it could contribute to the deposits 

on the limestone plateau.

COMPARISON OF SOILS OF GUAM WITH THOSE OF 

SIMILAR PARENTAGE IN OTHER SELECTED AREAS

The soils of Guam, with their parent rocks of basalt, 

tuffs, and limestones, are similar in appearance to those 

on the same kind of rocks undergoing weathering under 

tropical climates in various geographical locations. 

Many Pacific Ocean islands consist of a volcanic core 

flanked by limestone, and the soils on these islands are 

apparently similar to those of Guam, although, except 

for the islands of Hawaii, little detail is available. 

The West Indian islands of Jamaica and Hispaniola 

(Dominican and Haitiian Republics) have gibbsitic 

soils on limestones comparable with those of Guam.

VOLCANIC BOCK SOILS

HAWAIIAN ISLANDS

The soils of the Hawaiian Islands have been described 

in considerable detail chemically, and many mechanical 

analyses have been published (Hough and Byers, 1937; 

Hough and others, 1941; Sherman and others, 1948). 

The basalts of the Hawaiian Islands differ in chemical 

composition from the basaltic andesites and tuffs of 

Guam in containing less silica but more titania (table 

19). The soil profiles have developed under rainfall 

ranging from 18 to 273 inches (Hough and others, 1941, 

p. 1), and exceedingly young, young, and old soils have 

been recognized. The chemical composition of the 

soils reflects that of the rocks. The silica is combined 

in the various minerals in the rocks and consequently 

is more easily removed than if it were partly present 

as quartz. Accumulation of TiO2 is a characteristic 

feature, as it is in the Guam soils; but as the original 

rocks of Guam contain only 0.5 percent TiO2 , compared 

with 2.3 percent in the basalts of the Hawaiian Islands, 

the TiO2 content is never as great.

Hough and others (1941, p. 32) found that two kinds 

of soil profiles are developed on the basaltic rocks of the 

Hawaiian Islands: a uniform profile in which SiO2 , A12O3 , 

Fe2O3 and TiO2 do not vary more than 5 percent in the different soil horizons; and a podzolic profile in which the 

soil horizons are of different composition, with concentrations of TiO2 , Fe2O3 , and A12O3 in the upper part, 

with a consequent loss of SiO2 . It is considered that 

the podzolic profile, which has also been described by 

Sherman and his coworkers (1948) as a ferruginous 

latosol, is an older and more mature profile than the 

uniform profile. The podzolic profile may develop 

from the uniform profile with time.

Of the Guam soil, the Atate clay apparently is comparable with the uniform profile. Analyses (tables 

11-14) show that SiO2 has been removed, and that

A12O3 , Fe2O3 , and TiO2 accumulate toward the surface; 

but there is a gradual change, and no very marked 

horizons, such as occur in podzols, are present.

The Asan clay of Guam can probably be compared 

with the young uniform soils of the Hawaiian Islands. 

One of the principal differences between the Asan clay 

and the Atate clay is that the former has recognizable 

grains of heavy minerals throughout the profile, whereas 

the Atate clay shows a marked surface accumulation of 

magnetite and other opaques. This is a result of longcontinued soil-forming processes and is a feature of old 

soils. The Asan clay has montmorillonite as its principal clay mineral, whereas the Atate clay has halloysite 

or mixed-layered halloysite-montmorillonite and a little 

gibbsite.

The chemical composition of the colloidal fraction 

«2/i) of the Hawaiian Islands soil profiles that developed under different rainfall conditions varies in the 

SiO2-Al2O3 ratio (Hough and others, 1941; Tanada, 

1951), which indicates a change in clay minerals as 

follows:

montmorillonite >halloysite >gibbsite

As SiO2 is removed, montmorillonite is unable to 

retain its lattice structure and its place is taken by halloysite; the alumina released from halloysite by further 

depletion of SiO2 results in the presence of gibbsite or 

other aluminum oxide.

Both pH and organic matter content of the Guam 

soils have a trend similar to those of the Hawaiian 

Islands.

The clay minerals present in mature soils of the 

Hawaiian Islands belong to the kaolinite group (Dean, 

1947, p. 102) and the differential thermal analysis curves 

strongly suggest halloysite, although Dean (p. 104) has 

not identified this mineral. In a study of the weathering of olivine basalt by Sherman and Uehara (1956) the 

differential thermal analysis curves of the soil adjacent 

to the basalt also suggest halloysite. In situations 

where the removal of bases is slow or restricted, the 

first weathering product of olivine is a member of the 

montmorillonite group. The weathering rock at the 

base of profile S54-21 has mixed-layered montmorillonite-halloysite, and the Asan clay S54-23-1 contains 

montmorillonite.

NORFOLK ISLAND

Norfolk Island which is in the south Pacific Ocean 

(lat 29°3 /45 // S. and long 167°56 /29 // E.) has an area 

of 8,500 acres. It consists of a core of basalts and 

tuffs surrounded by limestone similar to Guam. The 

soils (Hutton and Stephens, 1956) have been described 

as krasnozems, and many soil types are distinguished, 

varying from dark red (2.5YR 4/4) to chocolate overlying a deep subsoil of red (10YR 4/5-4/6) (Munsell 

Color Co., Inc., 1954), compact but friable granular
MINERALOGY OF SELECTED SOILS F37

TABLE 19. Comparison of soils developed on basalt and volcanic ash from various selected localities

Soil description

GUAM

Lateritic, Atate clay. 

HAWAIIAN ISLANDS

NORFOLK ISLAND

Krasnozem,2 several soil 

types.

LISMORE, NEW SOUTH 

WALES, AUSTRALIA

Krasnozem,2 Alphadale 

clay loam.

INVERELL, NEW SOUTH 

WALES, AUSTRALIA

NORTHERN IRELAND

Type of 

profile

Uniform. - 

 do 

Uniform 

and podzolic.

Uniform . . 

...do 

 doRainfall 

(inches 

per 

year)

89 

89

1100 

53 

55

Temperature, 

mean (°F)

80 

80

75 

66 

67

Humidity 

(percent)

81 

81

68 

80

pH

5.3

7.4

6.4 

5.3

Cationexchange 

capacity 

(milliequivalents per 

100 

grams)

14.0

13.7 

22.5

Sum of 

exchangeable 

bases

1.2 

5.5

.7

1.8

Chemical composition (percent)

Si02

33.9 

45.0

22.2

15.4

16.9

20.7

A12 O3

28.4 

16.9

24.1

21.9

49.2

26.8

FeaOs

15.6 

10.0

25.8

29.7

19.6

28.3

Free 

Fe2O3

11.6 

4.1

14.3

10.6

Ti02

0.9 

.8

5.5 

7.3

10.6

3.5

H2 O

17.8 

18.6

17.6

20.6

13.3

Grain size (percent)

Sand

5.8 

7.3

13.6 

8.5 

11

Silt

23.5 

31.0

40.3 

15 

14

Clay

70.7 

61.7

43.0 

70 

72

Clay minerals

Halloysite, gibbsite, montmorillonite. 

Montmorillonite.

Kaolinite -group 

mineral, montmorillonite.

Kaolinite-group 

mineral, gibbsite.

Kaolinite, halloysite, rnontmorillonite.

Kaolinite, gibbsite.

Halloysite, 

chamosite, 

gibbsite, 

chlorite-type 

mineral.

1 Rainfall in the different islands is variable; it also varies from windward to leeward 

side and with elevation.

2 Krasnozem is a red loam, generally termed a "latosol" in the United States.

EXPLANATION

Guam soils:

Data for the Atate clay are averages obtained from 29 samples (6 profiles) for chemical analyses and 33 samples (6 profiles) for mechanical analyses.

Data for the Asan clay are averages obtained from 2 samples (1 profile). 

Hawaiian Islands:

Data are from Hough and Byers (1937) for the mechanical analyses (29 samples from 

6 profiles) and from Hough and others (1941) for the chemical analyses (45 samples 

from 11 profiles). The profiles are described as "young profiles" and "old profiles." 

The rainfall under which they have developed ranges from 20 to 273 in., average 99 

in. per year. 

Norfolk Island:

Data are from Stephens and Hutton (1954) and Hutton and Stephens (1956). 

Mechanical analyses are for 22 samples from 6 profiles developed on basalt; greatest 

depth of profile is 72 in. The chemical data are derived from those given by Hutton 

and Stephens (1956, p. 261) and are for 6 samples of 3 soil types to a depth of 38 in. on 

basalt.

clay to a depth of 60 inches. Other soils are brown, 

dark brown, or black, depending on topography and 

drainage. The rocks on which the soils have developed 

are not very deeply weathered. The recalculated 

chemical analyses (table 19) from Hutton and Stephens 

(1956, p. 261) show their similarity in development to 

the soils of Guam.

The soils of Norfolk Island are depleted in calcium, 

magnesium, and silica, with accumulation of iron and 

titanium to a depth of 30 inches. These soils have pH 

averaging 6.4, which is higher than that for the Atate 

clay (5.3). The incomplete rainfall records suggest 

that for several months during the year on the island 

there is an excess of rainfall over evapotranspiration

Lismore, New South Wales, Australia:

Data are from Nicolls and Tucker (1956). No chemical analyses are available, but 

the figures for mechanical analyses are averaged from 19 samples (3 profiles), 2 of which 

are to depths of 72 and 82 in., respectively, and the third to a depth of 189 in. (15.75 ft). 

Inverell, New South Wales, Australia:

Data are from Carroll and Woof (1951) from a single old or "fossil" laterite profile 

which was sampled to a depth of 23 ft. Chemical analyses are averages of 8 samples to 

this depth. 

Northern Ireland:

Data are from Eyles (1952) for the interbasal tic laterite which developed as a typical 

podzolic type of profile. The figures for the chemical analysis quoted were averaged 

from those quoted on page 14 (idem.) for a set of samples illustrating the lithomarge 

and laterite from basalt. The material at the surface of the old profile contains sufficient iron for it to be used as an iron ore.

(Hutton and Stephens, 1956, p. 262); so considerable 

leaching of the soils occurs.

The minerals in the clay fraction, to a depth of 30 

inches, are kaolin, goethite, hematite, and a little 

gibbsite; quartz and rutile were found in one sample. 

Gibbsite may be considered the principal mineral in 

the coarser fractions (Hutton and Stephens, 1956, p. 

263), for it is the dominant mineral identified in the 

concretionary material in many of the soil types. 

Mechanical analyses given by Stephens and Hutton 

(1954, p. 14-19) show that the surface soils in general 

contain a greater quantity of sand grades (2 to 0.2 

mm) than the surface soils of Guam. The total cationexchange capacities are very similar to those for the
F38 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

soils of Guam with calcium as the dominant exchangeable cation.

LISMORE, NEW SOUTH WALES

The soils developed on basalt in the Lismore district 

in the northern part of New South Wales, Australia, 

have been described by Nicolls and Tucker (1956). 

The area is near the coast and is part of an extensive 

basalt plateau in an advanced stage of dissection. The 

four residual soils on basalt are krasnozems, which are 

reddish-brown deep soils considered to be at an advanced stage of weathering which results in the production of kaolin minerals, goethite, and gibbsite. 

They have developed under a yearly rainfall of 55 to 

60 inches, mostly in summer. The sand fractions, as 

in the Guam soils, are small and variable, and the reaction is acid, averaging 5.3. The pH at the surface is 

higher than at depth, one profile having pH 4.2 at 96 

to 108 inches. The clay content is high but variable, 

and an accumulation of coarser particles may be in the 

surface soil.

The clay minerals of these soils have been examined 

in considerable detail by Norrish x as quoted by Nicolls 

and Tucker (1956, p. 51).

the silicate clay minerals of these krasnozems belong to the kaolin 

group and make up 70 to 95 percent of the clay mineral assemblage. In the deeper horizons the kaolin mineral is halloysite. Towards the surface the kaolin structure becomes increasingly well ordered, approaching that of kaolinite. The remainder 

of the clay consists of hematite and ilmenite (together 5 to 15 

percent of the clay) with a little gibbsite in the surface horizons 

and occasionally some quartz.

An interesting relation between free iron oxide and 

drainage has been noted by Nicolls and Tucker (1956, 

p. 115) who state, "The separation of iron (from the 

original minerals) as the free oxide is very important 

in maintaining the free internal drainage of the krasnozems" and hence favors their continued development.

In mechanical composition all the soils formed on 

basalt in the Lismore area have a large proportion of 

clay and, according to Nicolls and Tucker (1956, p. 

116),

this is most apparent in the krasnozems where all but the most 

resistant primary minerals have weathered to clay minerals. 

The smaller amounts of clay at the surface of the soils are probably due to a change in composition of the clay minerals rather 

than to movement of clay particles by eluviation. In the 

Caniaba series (pedocalcic black soils, residual on basalt) this 

change is from montmorillonites to kaolinite group minerals, 

and in the krasnozems it is from kaolinite group minerals to 

gibbsite; both these changes involve a loss of silica from the 

clay fraction.

A diagrammatic representation of the mineralogical 

changes accompanying the development of the various

i Norrish, Keith, 1952, A study of the mineralogy of some Australian soils formed 

from basic igneous rocks: Unpub. Ph. D. thesis (pt. 1), Univ. London.

soils of the Lismore area (Nicolls and Tucker, 1956, 

fig. 21, p. 116) has been adapted to show the relationship of the soils of Guam to the soil-forming processes 

as indicated by the chemical analyses (fig. 9). The 

positions of the soils of Guam to the soils of Hawaii, 

Norfolk Island, Lismore, Northern Ireland, and Inverell, New South Wales are shown.

INVERELL, NEW SOUTH WALES

A single profile of a laterite on basalt was described 

by Carroll and Woof (1951). It is an example of a 

podzolic profile in which there is a sharp contrast in 

chemical composition and mineralogy in the different 

horizons between the weathered parent rock and the 

bright red ferruginous soil. The normative composition of the fine earth «2 mm) from each horizon shows 

that kaolinite ranges from 72 percent in the red and 

white mottled zone (12.75 to 16.25 ft) to 6 percent in 

the bauxitic horizon just above it (11.5 to 12.75 ft), 

which contains 90 percent of gibbsite. X-ray examination confirms the calculations from the chemical 

analyses. Calculations show that a loss of 90 percent 

of the silica originally present in the parent basalt 

would produce a profile having approximately the composition that was found for the weighted average of 

the samples. Hematite is the principal iron oxide, but 

a little goethite also occurs. A marked concentration 

of TiO2 occurs in most horizons; it is largely present 

in ilmenite, but anatase is also present and is recorded 

by X-ray diffraction. The parent rock contains 1.13 

percent TiO2 . Maghemite, a magnetic hematite developed from magnetite, was found in the lower part 

of the profile; a similar occurrence of maghemite 

is recorded (Eyles, 1952, p. 34) for the laterites of 

Northern Ireland, which can be considered comparable in many ways.

ANTRIM, NORTHERN IRELAND

The chemical composition and mineralogy of the 

laterites of the Interbasaltic Horizon among the Tertiary basalt flows of County Antrim, Ireland, have 

been described in detail by Eyles (1952). The interval 

between basalt flows was sufficiently long to enable the 

lower basalts to weather to laterites and bauxites. 

Later, the weathered surface was covered by another 

flow of basalt.

Analysis are given (Eyles, 1952, table 1, p. 14) that 

show a progressive loss of SiO2 and an accumulation 

of A12O3 , Fe2O3 , and TiO2 in the weathering products 

of the basalt. The mineral composition calculated 

from the analyses gives about 70 percent kaolinite 

in what is described as basaltic lithomarge, and less 

than 2 percent kaolinite in red ferruginous bauxite 

containing 66 percent of gibbsite. Some of the weathered material contains sufficient iron to be used as
MINERALOGY OF SELECTED SOILS F39

an iron ore, the iron-bearing minerals being hematite, 

goethite, and magnetite. The material high in iron 

oxide forms an upper crust just above the bauxite 

horizon. Thus, this profile may be described as a 

podzolic one from the original description of Hough 

and others (1941, p. 34). It is similar to the laterites 

which have been described from India (Fox, 1932) and 

the "fossil" laterites from Australia (Carroll and Woof, 

1951; Prescott and Pendleton, 1952). Such lateritic 

profiles are characterized by morphological, chemical, 

and mineralogical distribution of their constituents in 

different easily recognizable horizons.

The process of removal of SiO2 and bases, leaving an 

accumulation of A12O3 , Fe2O3 , and TiO2 is similar to that 

of the soils of Guam, but the Antrim laterites are considered to be at a later stage of development.

X-ray examination of the Antrim laterites and bauxites has confirmed the presence of a kaolin-type mineral, 

gibbsite, goethite, boehmite, hematite, a chlorite-type 

mineral, anatase, rutile, and maghemite. The kaolintype mineral is halloysite, Al2O3 -2SiO2 -2H2O. Endellite, Al2O3 -2SiO2 -4H2O, was recognized in many of the 

samples investigated. Thus, the principal clay mineral 

of the soils of Guam is the same as that in the Antrim 

laterites.

Other similarities are the presence of hematite as the 

principal iron oxide, of gibbsite, and of small quantities 

of goethite and boehmite. Most of the magnetite in 

the Antrim laterites has been altered to hematite and 

some to maghemite, the latter not having been recognized in the soils of Guam.

Chamosite (Eyles, 1952, p. 47), a clay mineral with 

the composition of a ferruginous kaolinite (Al, Fe3+, 

Fe2+, Mg)3 (Si, A1)2O3 -2H2O, was found as a secondary 

alteration product in some parts of the Antrim laterites 

where downward-leaching water has reduced ferric to 

ferrous iron. Swampy conditions on the land surface 

are considered responsible for the leaching water.

The examples given above have been used to compare 

with the soils of Guam because considerable chemical 

and mineralogical detail are available. Many other 

soils developing on mafic rocks under warm temperatures and high rainfall conducive to rapid leaching and 

weathering show the same processes, namely, the removal of SiO2 and the accumulation of A12O3, Fe2O3 , 

and TiO2 . Descriptions in the literature indicate that 

there are many stages in the genesis of lateritic profiles. 

As the process continues, the pH decreases to a minimum determined by the environment, exchangeable 

cations are removed, and simpler clay minerals replace 

the more complex ones.

SOILS ON LIMESTONES

Red soils associated with limestones are a common 

feature in many places. Such soils vary in character

from strongly podzolized red soils to true laterites and 

from strongly acid soils to those high in free calcium 

carbonate (Baldwin and others, 1938, p. 991). Silicaalumina ratios vary from considerably more than two 

to much less than one. These red soils have been 

termed "terra rossa."

Red soils associated with limestones occur on a number of islands in the Pacific Ocean, on Jamaica and 

Hispaniola in the West Indies, and on islands in the 

Bahama group. Many of these islands have a central 

core of volcanic rocks that is flanked by limestone, but 

some, such as the Bahamas and Miyako and Aguiguan 

in the Pacific, do not.

Many of the limestones associated with terra rossa 

deposits of soillike and bauxitic material contain small 

quantities of volcanic-ash minerals and clay minerals 

derived from the weathering of volcanic rocks. These 

impurities are released as a residual deposit if the limestone is removed by solution during weathering. As 

most of the limestones are relatively pure, however, 

insoluble material apparently is insufficient to form 

thick deposits. It seems, therefore, that soil material 

of similar composition has been added from outside 

sources. Mineralogical examination of the limestones 

and the bauxitic soils of Jamaica by Hartman (1955) 

has shown that both limestones and soils contain the 

same suite of minerals. The aluminous lateritic soil 

of the Dominican Republic contains accessory minerals 

that are characteristic of volcanic material (Goldich 

and Bergquist, 1947, p. 77). These soils are derived 

wholly or in part from the solution of limestone.

The terra rossa type of bauxites are well known in 

southern France, Italy, Greece, Yugoslavia, and elsewhere (De Weisse, 1948; Harder, 1949). Similar 

types of bauxite deposits associated with limestone 

occur in the Valley and Ridge province of the southeastern United States.

The chemical composition of these bauxitic soils 

from different localities is rather similar. Marshall 

(1930) described red soils on the karstlike irregular 

surface of the makatea on Atiu Island, and similar 

soils are found on Mangaia Island. Analyses given 

below show typical features in a low percentage of 

silica and high percentages of alumina and ferric oxide.

A12 03 

Fe2 03 

CaO_

P2 05 ..___-_ 

Ignition lossTaunganui.

Atiu Island

(percent)

9. 80

23. 85

25. 13

2. 75

5.42

2. 55

30. 60

100. 10

Mangaia

Island 

(percent)

8. 84

19. 70

31. 71

1. 60

5. 10

2. 48

30.80

100. 23
F40 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

The formation of bauxite from clay and argillaceous 

terra rossa is shown by the following analyses (in 

percent) from Zans (paper presented at the Tnternat. 

Geol. Cong., 20th, Mexico City 1957).

SiOa - 

AljOi 

FejOa ~ 

TiOt.. _ . 

H»O - 

1

55.6

12.2

6.1

1.0

9.0

2

5.0

45.3

19.7

1.9

23.4

3

11.4

46.4

19.3

2.3

19.5

4

1.4

49.2

17.8

1.7

24.1

5

0.4-3.5

46. 4-50. 3

17. 5-22. 8

2. 4-2. 6

26.0-27.0

" NOTE. Minor elements are omitted.

1. Clay.

2. Bauxitic terra rossa or low-grade bauxite.

3. Bauxitic terra rossa or low-grade bauxite, about 1,000 ft above sea level.

4. Red bauxite, about 700 ft above sea level.

5. Red bauxite, average of commercial bauxite of Jamaica from higher limestone 

plateaus.

In discussing the origin of the bauxite of Jamaica, 

Zans points out the importance of the drainage through 

the limestone, and the height above the water table.

The aluminous lateritic soil in the Aceitillar area, 

Dominican Republic, analyzed by Goldich and Bergquist (1947, p. 65) has the following composition 

(average of 10 samples): SiO2, 2.45; A12O3, 47.61; Fe2O3, 

19.86; TiO2, 2.64; loss on ignition, 25.8 percent.

The principal mineral of the bauxite of the Dominican 

Republic is gibbsite, as it is in the bauxite of Jamaica 

and in the Guam clay on limestone. Boehmite and 

kaolinite are also present. Hematite is the chief iron 

mineral, but a little goethite is also present (Goldich 

and Bergquist, 1947, p. 68-69). The accessory minerals are quartz, zircon, and magnetite or ilmenite, and 

these accessories are similar to those in the aluminous 

lateritic soil from Haiti and from Jamaica. In another 

area (Bucan Polo) the silica content of these soils is 

higher and normative kaolinite or halloysite, ranging 

from 18 to 27 percent, has been calculated (p. 71). 

Although not completely identified, it is suggested that 

this clay mineral is halloysite.

Kaolinite and halloysite are the principal clay minerals in the Jamaica bauxite, according to Hill (1955, 

p. 680). Similarity between the mineralogy of the 

acid insoluble residue in the White Limestone and the 

bauxite suggests (p. 684) that this limestone is the 

immediate source of the bauxite even though this 

residue amounts to only one-half of 1 percent of the 

rock. The constituents in this residue are AI2O3, 

Fe2O3, SiO2, TiO2, and P2O5. Hartman (1955), from his 

study of the insoluble residues of limestone and bauxite, 

is of the same opinion as to its origin.

Soils considered to be terra rossa have recently been 

studied in Israel (Barshad and others, 1956) and in 

Australia (Norrish and Rogers, 1956; Stace, 1956; and 

Mclntyre, 1956). The clay content of these soils is 

high (average of 5 samples is 47.6 percent, Stace, 1956, 

p. 292) and the clay minerals are the same as those in 

the underlying limestone, although montmorillonite,

where present, has been replaced by kaolinite and (or) 

vermiculite (Norrish and Rogers, 1956, p. 296). Free 

iron oxide is a major constituent of these soils, as it is 

of the Guam clay. It causes aggregation of the grains, 

thereby increasing the porosity and the passage of 

water through the soil material. This effect is not 

completely understood (Mclntyre, 1956, p. 304). The 

aggregation may be due to iron oxide alone or to an 

iron-organic matter complex binding the particles 

together. Apparently organic matter is quickly broken 

down in this type of soil, and organic compounds are 

added to the soil solution.

In summary, the Guam clay, a red soil associated 

with the Barrigada and the- Mariana Limestones, is 

similar to some other red soils occurring in comparable 

geologic environments. Chemically and mineralogically it resembles the bauxites of Jamaica, the aluminous laterites of the Dominican Republic, and the red 

soils of Atiu and Mangaia Islands in the Pacific Ocean.

Several different kinds of soil are associated with 

different kinds of limestone on Guam. Some, such as 

the Agana Argillaceous Member of the Mariana Limestone, contain large quantities of clay derived from the 

weathering of volcanic rocks. In the rather pure 

Mariana Limestone, however, there are only very small 

quantities of clay minerals and of volcanic-rock 

minerals. Leaching of both types of minerals by surface 

waters at pH values a little below pH 7 removes silica 

preferentially to alumina, particularly from the clay 

minerals. Gibbsite therefore forms if the drainage is 

sufficiently good to transport silica away from altering 

clay minerals (largely halloysite). The iron oxide 

originally attached to the halloysite particles also 

accumulates because it cannot go into solution at 

neutral to slightly alkaline pH values. Gibbsite forms 

only very slowly in the relatively impermeable soils 

associated with the argillaceous limes tones. The clay 

mineral in these limestones is also halloysite. The 

argillaceous limestones weather in a similar manner to 

the volcanic rocks. A saprolite forms first, and then in 

its upper surface a soil develops. The amount of 

gibbsite in the soil on argillaceous limestone is comparable in amount to that in the soils formed from 

volcanic-rock materials.

CONCLUSIONS

The data from the mineralogical and chemical investigation of selected soil profiles on the volcanic rocks 

and on the limestones of Guam show that two distinct 

kinds of soils are associated with these rocks. The 

Atate clay on the volcanic rocks consists principally 

of halloysite, iron oxides, and a little gibbsite. The 

most widespread soil on the Mariana limestone, the 

Guam clay, consists principally of gibbsite, iron oxides,
MINERALOGY OF SELECTED SOILS F41

and a little boehmite and halloysite. The Guam clay is 

similar mineralogically and chemically to the terra 

rossa type of bauxite found in Jamaica.

The principal process of formation of both types of 

soil is the removal of silica by percolating waters. This 

is a lateritic type of weathering. Silica in the volcanic 

rocks is present in plagioclase feldspars, zeolites, glass, 

and pyroxenes. These minerals are all weather able, 

and consequently the volcanic rocks are weathered to 

considerable depths (more than 50 ft in places). Comparison of chemical analyses of fresh rocks and of 

saprolite many feet below the surface shows that silica 

has been removed. The average pH of the Atate clay 

is 5.3; the pH is lower at depth. Silica goes into solution 

at all pH values, but alumina and iron do not. They 

accumulate in the weathering rocks and soils.

The first mineralogical changes in the weathering of 

the volcanic rocks are feldspars, pyroxenes, glass, and 

zeolites to montmorillonite. Continued leaching of 

bases causes the montmorillonite structure to break 

down, and montniorillonite is replaced by halloysite. 

Ferric oxide is produced by the oxidation of ferrous iron 

in pyroxenes; ferric oxide coatings on clay and other 

mineral particles results. Continued leaching removes 

silica from halloysite and gibbsite is produced.

Comparison of the mineralogy and chemical composition of the Atate clay on Guam with lateritic soils 

developed on similar types of rock in other countries 

shows that various stages of development can be 

recognized. Sufficient climatic data are not available 

to assess the leaching factor that is responsible for the 

development of the Atate clay, but comparison with the 

lateritic soils (latosols) of the Hawaiian Islands indicates that the Atate soil is similar to the uniform 

profile soils. The relative accumulations of A12O3 , 

Fe2O3 , and TiO2 occur in both types. The volcanic 

rocks of Guam, however, contain somewhat more 

silica, and less iron and titania than the Hawaiian 

basaltic rocks. The rocks of Guam are more aiidesitic 

in character.

The presence of gibbsite in the red soils (Guam clay) 

associated with the Mariana Limestone is considered 

to be due to the removal of silica from clay minerals, 

such as halloysite and montmorillonite, by leaching with 

water at almost neutral pH. The average pH of these 

soils is 7.4. Ferric oxide, alumina, and titania are 

insoluble at this pH.

The insoluble residues of the limestones vary in 

quantity and in mineralogy. In some limestones the 

residue consists of volcanic minerals, such as augite, 

hypersthene, magnetite, feldspars, and zeolites. These 

minerals seem to come from volcanic ash falls over the 

area in which calcium carbonate was being deposited. 

In other limestone beds clay minerals and iron oxides

were deposited. These minerals came from the erosion 

of a land surface and were transported to the area of 

carbonate deposition. This material is similar to that 

in the deeply weathered volcanic rocks on Guam.

The volcanic minerals in these limestone remain 

unaltered until calcium carbonate is removed by solution. Alteration of glass and zeolites to clay minerals 

takes place if calcium carbonate is removed. The 

grain size of the Guam clay is coarser than that of the 

Atate clay, and the sand fractions contain volcanic 

minerals and some composite unweathered rock fragments. Mineralogical examination of a limestone soil 

on Mount Lamlam shows that the original detrital 

volcanic minerals alter first to montmorillonite. Silica 

is then removed and gibbsite forms without an intermediate halloysite stage. This suggests that, although 

the amount of fresh detritus in the Mariana Limestone 

is generally small, it contributes to the gibbsite present 

in the Guam clay. The scattered distribution of the 

detrital minerals in the limestone enhances their chances 

of rapid change to montmorillonite and then to gibbsite. In the argillaceous limestones, on the other hand, 

the clay minerals form thick beds that are less permeable to water, and the alteration proceeds slowly, as 

in the Atate clay associated with the volcanic rocks. 

The Asan clay on the Agana Argillaceous Member of 

the Mariana Limestone is an example of this type of 

development.

The small quantity of detrital material, both fresh 

volcanic minerals and clay minerals, makes it difficult 

to explain the amount of red soil that is associated with 

the Mariana Limestone. It is probable that soil 

material from the weathered volcanic rocks on Guam 

has been deposited on the surface of the northern limestone plateau. This material together with that in the 

limestones has been leached in a porous near-neutral 

environment to produce the red gibbsitic deposits. The 

fact that the titania content of these soils and of 

bauxites on limestones from many widely separated 

areas is about 2 percent indicates that the processes 

operating on residual material in the limestones, or 

associated with the limestones, must be similar, and 

that the material has a narrow range of composition. 

The composition may be characteristic of an "average 

clay."

The following schematic sequence of events is suggested as an explanation of clay mineral development in 

the soils associated with limestones:

Detrital volcanic minerals k montmorillonite » gibbsite > boehmite 

Incorporated soil minerals > halloysite » gibbsite * boehmite

The change from gibbsite (3H2O) to boehmite (H2O) is 

thought to be due to the periodic desiccation of these 

soils, as drainage is rapid even after heavy falls of rain.
F42 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

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Prescott, J. A., and Pendleton, R. L., 1952, Laterite and lateritic 

soils: Commonwealth Bur. Soil Sci. Tech. Commun. 7, 51 p.

Reiche, Parry, 1950, A survey of weathering processes and products: New Mexico Univ. Pub. Geology 3, 95 p.

Schlanger, S. O., 1963, Petrology of the limestones of Guam: 

U.S. Geol. Survey Prof. Paper 403-D (in press).

Sherman, G. D., Foster, Z. C., and Fujimoto, C. K., 1948, Some 

properties of the ferruginous humic latosols of the Hawaiian 

Islands: Soil Sci. Soc. Am. Proc., v. 13, p. 471-476.

Sherman, G. D., and Uehara, Goro, 1956, The weathering of 

olivine basalt in Hawaii and its pedogenic significance: 

Soil Sci. Soc. Am. Proc., v. 20, p. 337-340.

Siever, Raymond, 1957, The silica budget in the sedimentary 

cycle: Am. Mineralogist, v. 42, p. 821-841.

Stace, H. C. T., 1956, Chemical characteristics of Terra Rossas 

and Rendzinas of South Australia: Jour. Soil Sci., v. 7, p. 

280-293.

Stark, J. T., 1963, Petrology of the volcanic rocks of Guam: 

U.S. Geol. Survey Prof. Paper 403-C (in press).

Stephens, C. G., and Hutton, J. T., 1954, A soil and land-use 

study of the Australian Territory of Norfolk Island, South 

Pacific Ocean: Commonwealth Sci. Indus, Research Organization, Australia Soils and Land-use Ser. 12, 28 p.

Tanada, Takuma, 1951, Certain properties of the inorganic colloidal fraction of Hawaiian soils: Jour. Soil Sci., v. 2, p. 83- 

96.
MINERALOGY OF SELECTED SOILS F43

Tracey, J. I., Jr., Schlanger, S. O., Stark, J. T., Doan, D. B., 

and May, H. G., 1963, General geology of Guam: U.S. 

Geol. Survey Prof. Paper 403-A (in press).

Zans, V. A., 1952, Bauxite resources of Jamaica and their development: Colonial Geology and Mineral Resources, v. 3, p. 

307-333.

DESCRIPTION OF SOIL PROFILES 1

By CARL H. STENSLAND 

SOILS OF VOLCANIC ROCKS

Profile S54-4. Atate day, on Alutom Formation

Location. About 1 mile southwest of ComNavMar headquarters (lat 13° 27' 21" N., long 144°42'18" E.), at a point 

near south-center of a fairly large mesita, about 500 ft northeast of junction of El Patio Road with Spruance Drive.

Topography. Upland flat (alt about 390 ft) rising 10 to 50 ft 

above surrounding terrain, about half an acre in area. Surface gradient across sampling area is about 1 percent.

Vegetation. Sword grass (Miscanthus floridulus) and scattered 

clumps of Casuarina equisetifolia; some Dimeria and other 

grasses and small shrubs.

Sample 

S54-4-1

Depth 

0-6 in.

4-2 6-20 in.

4-3 20-30 in.

4-4 30-51 in.

4-5 51-60 in.

Description

Dark-reddish-brown (SYR 3/3 2 

dry, to 2/4 moist) clay; strong 

fine granular to medium granular 

in upper half-inch of soil and 

medium granular below (granules are hard when dry, and waterstable); friable to firm and only 

slightly sticky; moderate plasticity; pH 6.O.3

Dark-reddish-brown (4YR 3/4 dry, 

2.SYR 2/4 moist) clay; structure 

and consistency same as sample 

4-1; contains roots and rootlet 

channels; pH 5.7. The lowest 4 

in. is gradational to the horizon 

below and was omitted from the 

sampling.

Dark-reddish-brown (2.5YR 3/4, 

moist) clay, similar to sample 4-2 

in structure; pH 6.0 to 6.5. 

Grades into underlying horizon.

Dark-red (2.SYR 3/6, moist) clay; 

contains yellowish-red spots (SYR 

5/6) that increase in number and 

size with depth; firm, with a few 

pinholes and small fractures, but 

less porous than upper horizons; 

pH about 6.

Red to reddish yellow (2.5YR 4/6 to 

SYR 6/6 moist) clay; less firm 

and more friable than upper 

horizons; pH 5.5 to 6.0.

1 The field positions of the profiles are shown on figure 3.

2 Color according to the Munsell Soil Color Chart, Munsell Color Co., Inc. (1954).

3 All pH values in these descriptions were determined in the field.

Profile S54-4 Continued

Sample 

S54-4-6

Depth 

11.0-11.5 ft

4-7 12.5-13.0 ft

Description

Varicolored soft porous clay, predominantly pinkish-white, with 

yellowish brown staining (the 

inside of each particle is mostly 

white, and the outside coating 

is pinkish); contains a few small 

hard vitreous granules; pH 5.0.

White to pale-yellow clay; soft 

porous coarse granular pyroclastic 

material (volcanic agglomerate 

and tuff), weathered to clay with 

bedding and structure preserved 

(saprolite); contains much red 

and pale-red material with bluish, 

greenish, and yellowish brown 

staining, the latter accumulated 

in individual particles in some 

places; pH less than 5.0. (Samples 4-6 and 4-7 were collected 

from one side of the scarp surrounding the mesita.)

Profile S54-5. Atate day, on Alutom Formation

Location. About 2 miles northwest of center of Yona village 

(lat 13°25'20" N., long 144°44'49" E.), on highest small 

mesita 300 ft northwest of jeep road to dismantled radio station, 2,500 ft southwest of station site.

Topography. Small upland flat (alt about 450 ft) with slightly 

convex surface sloping northwestward at about 3 to 5 percent 

gradient; bounded by scarps 10 to 30 ft above the surrounding 

terrain.

Vegetation. Miscanthus floridulus and scattered Casuarina 

equisetifolia.

Sample Depth Description 

S54-5-1 0-6 in. Dark-reddish-brown (5YR 3/3, dry)

clay; very fine grained, subangular 

blocky; very hard; noncalcareous; 

some "bauxitic" concretions 

(rounded to angular, pitted, pinkish-white fragments, 2 to 10 mm 

diameter) and some fine' eggshaped black pellets (iron, manganese or both, less than 1 mm 

diameter), and a few very fine 

threads or fibers of a glassy mineral; porous; many small roots; 

pH 5.5 to 6.0. The lowest 3 in. 

is irregularly transitional to the 

horizon below.

5-2 6-18 in. Red (10R 5/6 to 2.5YR 3/5, dry) 

clay; moderately fine, blocky; 

firm; slightly sticky; contains some 

irregularly pitted concretions (1 

to 10 mm) of a whitish mineral 

that becomes more abundant in 

the lower part of this horizon; 

contains a few small pinholes and 

root hairs; pH 5.0.
F44 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

5-4 53-60+ in.

5-5 10. 0-10. 5 ft

5-6 28. 5-29. 0 ft

Profile S54-5 Continued

Sample Depth Description 

S54-5-3 18-53 in. Similar to overlying horizon, but

whitish concretions comprise as 

much as 5 percent of volume.

Red (10R 3/6, dry) moderately fine 

clay; finely mottled with light 

gray and bright yellow; very few 

concretions; fine tubes numerous; 

pH 5.0.

Red (7.5R 4/6, dry) clay; strong, 

fine subangular blocky to coarse 

granular or nutty; hard; plastic; 

sticky; porous, with numerous 

cracks and fractures; contains a 

few distinct fine white mottles; 

pH 4.5 to 5.0.

Soft highly weathered tuff; white in 

a 2-mm layer bordering joints or 

fractures, and reddish-yellow 

(7.5YR 7/6, dry) clay; each fracture zone is coated with weak-red 

(10R 4/4, dry) material. The 

weathered tuff breaks readily into 

angular blocks, but is very hard 

when dry; pH 4.5 to 5.0. The 

underlying rock is tilted bedded 

fine- to coarse-grained "sandy" 

tuff, weathered to clay to depths 

of 50 ft or more. It is stained 

red almost throughout to depths 

of 6 to 10 ft and is red in bands 

along bedding planes and fractures 

to depths of 20 to 30 ft. 

(Samples 5-1 to 5-4 were collected from a 5-ft test trench; 

samples 5-5 and 5-6 were collected from a scarp of the mesita.)

Profile S54-6. Atate clay, on Bolanos Pyroclastic Member of the 

Umatac Formation

Location. About 2.85 miles south of center of Talofofo village 

(lat 13°18'38" N., long 144°44'45" E.), and about 1 mile 

west of paved highway (Yona to Inarajan), along north side 

of road through Martinez pasture, 100 yd east of concrete 

house on high gently sloping ridge.

Topography. Narrow upland flat or mesita (alt about 330 ft) 

with about 4 percent eastward slope; nearly vertical scarps 

rise 10 to 25 ft above erosion-scarred terrain immediately 

adjacent to the mesita.

Vegetation. Chiefly Dimeria in soft-tufted small clumps, and 

clumps of Lemonchina and Pandanus.

Profile S54-6 Continued

Sample Depth Description 

S54-6-1 0-2 in. Dark-reddish-brown (5YR 3/3, dry)

clay; strong fine granular to coarse 

subangular blocky; hard; porous; 

some limonite pellets and subangular concretions (1 to 8 mm 

diameter); numerous small roots 

and few larger ones; pH 6.0.

6-2 2-10 in. Dark-reddish-brown (5YR 3/4, dry) 

clay; coarse subangular blocky; 

hard; slightly to moderately plastic; numerous fine «0.5 mm diameter) grains of magnetite and 

some pellets of limonite (2 to 3 

mm diameter); a few small (0.5 

to 5.0 mm diameter) pitted concretions of a whitish mineral; porous; numerous pinholes and small 

joints; small roots; pH 5.5.

6-3 10-16 in. Mixed dark-reddish-brown and darkred clay, gradational to horizon 

below.

6-4 16-32 in. Dark-red (2.5YR 3/6, dry) clay; 

very firm; plastic; hard when dry ; 

numerous small joints or fracture 

faces; several small soft rounded 

grains of white light-gray and 

pale-yellow clayey material; some 

hard pitted whitish concretions; 

numerous small black hard grains 

or crystals of magnetite, and 

some soft grains, probably manganese; pH 5.0.

6-5 32-46 in. Dark-red (2.5YR 3/6, moist) to red 

(2.5YR 4/6, moist) clay; firm; 

slightly plastic; porous; similar to 

overlying horizon, black grains 

less numerous; whitish concretions 

as much as 10 mm diameter; 

pH 5.0.

6-6 46-60 in. Faintly banded (1 to 2 in. width) 

red and dark-red clay; moderately 

firm to slightly friable; few small 

black grains in dark-red parts; 

few small soft white, pale-yellow, 

and light-yellowish-brown grains 

throughout; soft ped faces have 

glistening soapy appearance; porous; few small root hairs; pH 5.0.
MINERALOGY OF SELECTED SOILS F45

Profile S54-6 Continued

Sample Depth Description 

S54-6-7 13. 5-14. 5 ft Red (7.5R 4/6, dry) clay; some original tuff structure preserved; distinct layers of light-red (7.5R 6/6, 

dry) clay common; white grains 

numerous throughout, concentrated in some layers giving 

banded appearance; pH 4.5. 

The underlying material is fine- to 

coarse-grained "sandy" tuff and 

agglomerate, mostly weathered to 

clay to a depth of 65 ft. 

(Samples 6-1 to 6-6 were collected 

from a 5-ft test trench; sample 

6-7 was collected from the scarp 

below the trench.)

Profile S54-10. Atate day, on Bolanos Pyroclastic Member of 

the Umatac Formation

Location. About 4 miles northwest of Talofofo Bay (lat 

13°17'10" N., long 144°44'19" E.) and about 0.8 mile northwest of the village of Inarajan, on a mesita about one-third 

mile southeast of the Inarajan water-point, 700 ft south of the 

road leading to the water-point from Inarajan village. 

Topography. Upland flat or mesita (alt 270 ft) about 5 ft higher 

than the eroded terrain immediately adjacent; mesita surface 

slopes at about 4 percent in a north-northwest direction. 

Vegetation. Thick stand of Miscanthus ftoridulus and some 

Stachytorpheta indica.

Sample Depth Description 

S54-10-1 0-3 in. Dark-reddish-brown (5YR 3/3, dry)

clay; granular to subangular 

blocky; slightly friable; hard; dark 

coloring largely due to organic 

matter; contains many roots; pH 

5.5 to 6.0.

10-2 3-15 in. Dark-red (2.5YR 3/6, dry) clay; 

medium-subangular blocky; very 

hard; contains many roots and 

some animal burrows as large as 5 

mm diameter; pH 5.0.

10-3 15-28 in. Red (10R 4/8, dry; 2.5YR 4/8, moist) 

clay of soft lapilli basalt or pyroclastic weathered material; slightly 

hard; slightly friable; contains 

many faint to prominent mottles 

that vary in color from dark red 

(2.5YR 3/6, dry) to yellow (10YR 

8/6 dry, to 7/8 dry) with some light 

gray; slightly plastic; pH 5.0.

Profile S54-10 Continued

Sample Depth Description 

S54-10-4 28-60+in. Dark-red (10YR 3/6, moist) clay,

with some of the original rock 

structure preserved or visible in 

outline; weak medium-subangular 

blocky to massive; friable; slightly 

plastic; contains some soft zeolitic(?) material and iron oxide 

staining; pH 5.0 to 5.5.

10-5 11. 3-12. 3 ft Red (2.5YR 4/6, dry) tuffaceous agglomerate, now weathered to clay; 

soft; slightly plastic; sticky; contains many medium-sized white, 

purple, and blue mottles; material 

expands appreciably when wetted; 

pH 5.0. (Samples 10-1 to 10-4 

were collected from a 5-ft test 

trench; sample 10-5 was collected 

from eroded scarp below trench).

Profile S54-12. Atate clay, on Facpi Volcanic Member of Umatac 

Formation.

Location. About 2.5 miles south of center of Agat village (lat 

13°21'4" N., long 144°39'0" E.), on first high mesita about 

100 yards south of the area known as "Agat dump." 

Topography. A narrow mesita (alt about 480 ft) with nearly 

vertical erosional escarpment on three sides rising to 15 to 65 

ft above severely erroded terrain immediately adjacent; the 

surface at the sampling site slopes westward at about 3 percent 

gradient.

Vegetation. Scattered clumps of Miscanthus floridulus and 

Dimeria, with Casuarina equisetifolia, Glochidion sp., Phyllanthus simplex, Myrtella benningsenniana, Gleichenia linearis, 

and a grass (Cladium sp.?).

Sample Depth Description 

S54-12-1 0-6 in. Dark-reddish-brown (5YR 3/4, dry)

clay; granular; hard; porous; numerous roots; contains some small 

white grains or crystals, and some 

small soft black concretions, 

mostly all less than 1 mm diameter; pH 5.5 to 6.0.

12-2 6-13 in. Reddish-brown (2.5YR 4/4, moist) 

clay; strong granular to subangular blocky; firm to friable; several 

cracks, fractures, and pinholes (1 

to 2 mm diameter) contributing 

to porous condition; some soft 

black concretions «1 mm diameter) ; pH 5.5 to 6.0.
F46 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

12-4 40-48+ in.

12-5 9. 0-10. 0 ft

Profile S54-12 Continued

Sample Depth Description 

S54-12-3 13-40 in. Dark-reddish-brown (2.5YR 5/4,

moist) clay; firm to friable; 

slightly plastic; porous; numerous 

fractures, pores and larger holes 

made by worms or roots; soft, 

powdery black film or coatings on 

20 to 30 percent of the peds, 

fracture faces, and inside holes 

(this condition is more pronounced 

in the lower part); pH 6.5.

Dark-red (2.5YR 3/5, moist) clay; 

moderately strong granular; friable; contains numerous small 

(<Cl mm diameter) pinholes or 

pores; some grains or aggregates 

of grains are light gray, pale 

yellow, and yellowish red; small 

black flecks «0.5 mm diameter) 

and black coatings on some grains 

and in some pores; a few root holes 

or channels (2 to 3 mm diameter); 

pH 6.5.

Weak-red (10R 5/4, dry) clay with 

pillow basalt structure preserved; 

contains many faint fine mottles 

of various shades of purple, red, 

yellow, and brown; soft to slightly 

hard when dry; sticky and slightly 

plastic when wet; porous; pH 5.0.

Pillow basalt weathered to clay; the 

overall color of the clayey matrix 

is pale red, with spots, splotches;, 

coatings, and veins of dusky red, 

purple, brown, yellow, and black; 

blocky; soft when dry; sticky and 

plastic when wet; porous; pH 4.5 

to 5.0. Underlying material is 

saprolitic pillow basalt weathered 

to a depth of 75 ft or more. 

Outlines of pillows are visible in 

the saprolite of the mesita escarpment downward from about 8 to 

10 ft below the top of the mesita. 

(Samples 12-1 to 12-4 were collected 

from a 5-ft test trench; samples 

12-5 and 12-8 were collected from 

the side of the mesita scarp.)

Profile S54-20. Atate clay, on Alutom Formation

Location About 0.7 mile northwest of Yigo Baptist Church 

(lat 13°32'39" N., long 144°52'47" E.). The site is found 

by traveling a quarter of a mile north along the Yigo-Anderson 

Air Force Base paved highway, turning left onto jeep trail 

for about 0.65 mile to a point 100 ft west of east end of crest 

of Mount Mataguac.

Topography Gently rounded ridge crest (alt about 750 ft) 

with a gradient of 2 to 8 percent, about 50 to 60 ft above 

lowest adjacent terrain.

Vegetation Scattered coconut, Chinese inkberry, Hibiscus 

tileaceous, Leucaena glauca, Hyptis pectinata, Penesetum 

polystachium, fern, and numerous weeds, grasses, vines, and 

shrubs.

12-8 22.5-23.0 ft

Profile S54-20 Continued

Sample Depth 

S54-20-1 0-4 in.

20-2 4-16 in.

20-3 16-36 in.

Description

Dark-reddish-brown (SYR 3/2, dry) 

clay; some granular structure, but 

mostly fine to coarse subangular 

blocky; hard when dry; friable 

when moist; slightly to moderately 

plastic when wet; contains numerous roots and is somewhat porous 

because of root penetration; soil 

cracks when dry, cracks being 2 to 

8 mm wide and penetrating to 

depths of 30 to 36 in. (Pieces of 

limestone ranging from 1 to 10 in. 

in diameter have probably been 

carried there by man); pH about 

7.0.

Red (2.5YR 4/6) clay; fine to coarse 

subangular blocky; moderately 

firm and very plastic; dark-reddish-brown staining on soil peds 

and fracture faces; vertical cracks, 

worm holes, and root channels 

show fillings of soil from surface 

horizon (earth worms are more 

numerous than in most soils sampled on Guam). The soil is fairly 

fine and compact between the 

holes, cracks, and crevices, but has 

small pinholes; pH 6.0.

Red (10R 4/6, moist) clay, with increasing amounts of weak-red 

(7.5R 5/4, moist) and pale-red 

(10R 6/2, moist), and light-gray 

saprolitic tuff; subangular blocks 

ranging from 0.5 to 3 in. in diameter; moderately firm; very plastic; 

numerous pinholes and fractures, 

some with yellowish-brown and 

light-gray staining; many fine 

joints in the tuff filled with paperthin red staining; some pink (5YR 

7/3, moist) tuff near base of horizon; finely porous; pH 5.0. The 

underlying material consists of 

water-laid volcanic ash and basaltic pyroclastics, now almost completely weathered to a depth of 

more than 50 ft.

Profile S54-21. Atate clay, on Alutom Formation

Location. About 1.5 miles east-northeast of Yigo village (lat 

13°32'22" N., long 144°52'49" E.), 0.82 mile north of intersection of Yigo road with new blacktop (BPM) highway, and 

about 550 ft east-southeast of the highway, on a mesita on 

the western slope of Mount Santa Rosa.

Topography. Gently concave narrow upland ridge crest (alt 

about 630 ft) with steep erosional scarps on 3 sides; slope of 

surface N. 55° W. at prevailing gradient of 6 to 7 percent; 

local relief about 25 to 50 ft.

Vegetation. Miscanthus floridulu*, Scaevola frutescens, Hyptis 

pectinata, a small sedge, a low creeping grass.
MINERALOGY OF SELECTED SOILS F47

Profile S54-21 Continued

Sample 

S54-21-1

Depth 

0-16 in.

21-2 16-36 in.

21-3 36-66 in.

21-4 8. 0-9. 0 ft

Description

Dark-reddish-brown (SYR 3/4, dry) 

clay; very fine to fine granular 

structure; hard; friable; slightly 

plastic; porous, with cracks, worm 

and root holes; roots and root 

hairs numerous; some pieces (floaters) of hard to soft light-yellowish 

brown (2.5YR 6/4, dry) weathered 

clayey tuff (0.25 to 1 in. diameter), 

with greenish and reddish-brown 

phenocrysts; a few small (<Cl mm 

diameter) soft black concretions; 

pH 6.0.

Red (2.5YR 4/6, moist) clay; medium-subangular blocky; firm; plastic; numerous pinholes or small 

root channels; some red (7.5R) 

and weak-red to pale-red soft tuff 

in the lowest 2 in.; pH 5.5.

Consists of about equal parts red 

clay as above and soft weak-red, 

pale-red, pink to pale-yellow grains 

of tuff weathered to clay; massive 

to columnar jointed; hard to firm 

when dry, friable when moist; 

feels somewhat "greasy" and "sandy," but grittiness is probably due 

to powdery manganese concretionary or joint-filling material; 

pH 5.0.

Saprolitic tuff; fine to coarse granular 

to massive; firm to friable; slightly 

plastic; chiefly bright red, yellowish brown, yellow and black; pH 

5.0.

Underlying material is massive 

fine- to coarse-grained tuff weathered to clay to a depth of 50 ft or 

more, but with original texture 

and structure preserved up to the 

soil solum. (Samples were collected from a trench, 1 by 1% by 

10 ft, cut vertically down the 

scarp face from the surface of the 

mesita.)

Profile S54 23. Asan clay, on Alutom Formation

Location. About 1 mile southwest of ComNavMar Headquarters Command building (lat 13°26'54" N., long 144°42'57" 

E.), along north side of pipeline road, about 1,500 ft east of its 

intersection with the Mount Tenjo road, 0.8 mile south of 

Spruance Drive.

Topography. Convex ridge top (alt about 540 ft) of low to 

intermediate height in gently sloping to rolling terrain; surface 

gradient about 3 percent at point of sampling. 

Vegetation. Miscanth us floridulu s.

Sample Depth Description 

S54-23-1 0- 8 in. Dark-grayish-brown (10YR 4/2.2,

dry) clay; coarse granular to 

coarse subangular blocky; hard 

when dry; contains pale-yellow 

spots (<1 mm diameter), and has 

numerous soft reddish-yellow to 

yellowish-brown (7.5YR 6/8, dry) 

stained lapilli or concretions (4 to 

15 mm diameter); pH 5.5 to 6.0. 

Changes abruptly to horizon below.

23-2 8-36 in. Pale-yellow (5Y 7/4, dry) to paleolive (5Y 6/4) and greenish clay, 

with^dark-red (2.5YR 3/6, dry) and 

dark-reddish-brown thin coatings 

or staining on some fracture faces. 

The different shades of yellow clay 

seem to be alteration patches in the 

greenish or olive matrix; coarse 

subangular blocky to massive; 

some small lapilli or pellets of pink 

or weak-red clay in the olive matrix, and some very dark-gray 

lapilli ()4 in. diameter) with small 

pale-yellow inclusions; coatings or 

film of dark-red on some fracture 

faces and some red has penetrated 

into the soft interior of angular 

pieces broken during excavation; 

hard when dry; pH 5.5 to 6.0. 

The underlying material is a massive lapilli pyroclastic rock, now a 

saprolite to a depth of 30 ft or 

more. (Samples were collected 

from a 2- by 3-ft channel cut back 

in roadcut.)
F48 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS

SOILS ON LIMESTONE

Profile S54-16. Guam clay, red latosol, on Barrigada Limestone

Location. About 1.75 miles southwest of Northwest Airfield 

(lat 13°35'05" N., long 144°51'15" E.), about half a mile southwest of Potts Junction, and 0.1 mile northwest of paved road 

which runs southwest to the Naval Communications Station 

area.

Topography. Long narrow shallow depressed area (alt about 

500 ft) in undulating limestone plateau; prevailing surface 

gradient less than 3 percent at sampling site. 

Vegetation. Coconut, papaya, Pasiflora foetida, Artocarpus sp., 

Chinese inkberry (Cestrum diurnum), and a fern. 

Sample Depth Description 

S54-16-1 0-60 in. Dusky-red (10R 3/3, moist) clay;

surface soil is loose, medium to 

coarse granular; weak to moderate 

subangular structure; somewhat 

plastic and sticky when wet; porous, dries out rapidly after heavy 

rain. Contains a few limestone 

floaters; pH 6.5 to 7.0. The soil 

is 31 ft deep where sampled, and 

represents a soil-filled limestonefissure condition that is somewhat 

common in areas of Guam clay. 

The underlying bedrock is exposed 

within 50 ft of the sampling site. 

Sample S54-16-2 is white hard 

porous limestone that is the presumed parent material of the soil.)

Profile S54-17. Guam clay, on Mariana Limestone, detrital fades

Location. About 5 miles east-southeast of Agana (lat 13°27'46" 

N., long 144°49'44" E.), and 1.55 miles N. 15° E. of Fadian 

Point, on the central east coast of Guam.

Topography. Flat to microundulating relief (alt about 320 ft), 

near edge of small shallow limestone sink; slope is less than 

3 percent at sampling site.

Vegetation. Hibiscus liliaceous, Artocarpus sp., Cestrum 

diurnum, Penisetum polystachium, Leucaena glauca, pandanus

Sample Depth Description 

S54-17-1 0-3 in. Dark-reddish-brown (2.5YR 3/4,

dry) clay; moderate medium to 

coarse granular; soft to slightly 

hard when dry; friable when moist; 

sticky and plastic when wet; contains numerous roots; pH 7.0 to 

8.0.

17-2 3-24 in. Dusky-red (10R 3/3, dry) clay; 

weak medium-subangular blocky 

structure; friable when moist; 

porous; numerous earthworm burrows; 1 coral fragment (4 in. 

diameter) at 10 in. depth; pH 8.0. 

(Sample S54-17-3 is quarry-run 

Mariana Limestone, Dean Bros, 

quarry, Tamuning; white, very 

porous hard lagoonal limestone is 

presumed parent material of soil.)

Profile S54-18. Guam clay, on Mariana Limestone, molluscan

fades

Location. Two miles \vest of the southern end of Anderson Air 

Force base (lat 13°31'39" N., long 144°52'47" E.), half a 

mile south of the center of Agafa Gumas camp area, near 

edge of shallow limestone sink-basin, 25 ft north of jeep road, 

at south edge of small farm clearing.

Topography. Undulating upland plateau (alt about 500 ft); 

range of surface gradient 1 to 8 percent, but about 3 percent 

at sampling site.

Vegetation. Pandanus, scattered ifilwood, banyan, and other 

trees, a few cycads, morning glory, and weeds.

Sample Depth Description 

S54-18-1 0-1 in. Dark-red (2.5YR 3/6, dry) clay; very

fine to coarse granular; hard when 

dry; friable when moist; some very 

dark-gray to black coatings on 

many of the peds or granules; 

porous; contains some root fibers; 

pH 7.5.

18-2 1-15 in. Dark-red (2.5YR 3/6, dry) clay; very 

fine granular friable; porous; contains a few roots; and some small 

powdery, white limestone particles; pH 7.0. Rest on limestone 

surface. (Sample S54-18-3, extending from 15 in. to unknown 

depth, is white (10YR 8/2, dry) 

limestone containing many large 

molluscan fossils; porous, especially in cavities or cracks between the 

fossils; some weak-red to lightreddish-brown soil adhering to the 

rock surface. This rock is the 

molluscan facies of the Mariana 

Limestone.)

Profile S54-19. Guam clay, on Mariana Limestone, reef facies

Location. At a point 1,600 ft northeast of the northwest corner 

of Northwest Airfield (lat 13°38'06" N., long 144°52'05" E.).

Topography. Gently sloping limestone plateau (alt about 510 

ft); surface gradient about 2 to 3 percent at sampling site.

Vegetation. Scattered ifilwood, pandanus, and casuarina 

trees, a few shrubs and some grass and vines.

Sample Depth Description

S54-19-1 0-4 in. Yellowish-red (5YR 4/6, dry) clay;

strong very fine granular; some 

dark-reddish-brown coatings; soft; 

friable; porous; contains some 

pieces of white limestone as much 

as 8 mm diameter, and some small 

pieces of charcoal, wood, and plant 

fibers; pH 7.0.
MINERALOGY OF SELECTED SOILS F49

Profile S54-19 Continued

Sample Depth Description 

S54-19-2 4-12 in. Red (4YR 4/6, dry) clay; very fine

granules; soft to moderately hard; 

friable; contains several pieces of 

pitted white limestone «0.5 to 

50 mm diameter); some roots; 

pH 8.0. (Sample S54-19-3, from 

12 to more than 20 in., is hard 

white dense to porous limestone 

with some white powdery material 

on newly broken faces; some small 

irregularly shaped cavities as much 

as 0.5-in. diameter.)

Profile S54-24. Fossil latosol, on Alifan Limestone, overlain by 

5 ft of the Agana Argillaceous Member of the Mariana Limestone.

Location. About 0.6 mile south of Sinajana village (lat 

13°26'57" N., long 144°45'25" E.), on east roadcut along 

main paved highway (site is just before first east farm road 

intersection near top of hill south of the river bridge.)

Topography. Narrow convex ridge (alt about 150 ft) through 

which there is a steep highway cut.

Vegetation. Leucanea glauca and lemonchina. 

Sample ' Depth Description

S54-24-1 Red (2.SYR 4/8, dry) clay; columnar blocky; very hard when dry; 

friable when moist; slightly porous 

with numerous vertical small fractures and pinholes; one roundish 

whitish concretion (2 to 3 mm diameter) possibly is chalcedony; 

numerous small pieces of magnetite 

or manganese; small slickensides 

on vertical columnar fracture 

faces; pH 8.0. A 1-in. band of 

distinct yellowish-brown clay at 

base of the red clay, at contact 

with the underlying Alifan Limestone, a hard dense pinkish-white 

limestone with fossil cavities (cavities 

partly filled with fossils or casts), 

some containing red to reddishbrown soft silt or rust; some limestone appears bedded, and some 

appears to be in the shape of large 

"heads" or boulders. The limestone overlying the fossil latosol 

has a foot or two of soil on it, consisting of 6 to 8 in. of dark-grayishbrown clay over brown to strong 

brown, firm plastic clay.

Profile S54-1. Chacha day, on Agana Argillaceous Member of 

the Mariana Limestone

Location. About 2.5 miles east-southeast of Agana (lat 

13°27'51" N., long 144°48'25" E.), at a point a quarter of a 

mile south of the highway, half a mile east of Barrigada 

village main intersection.

1 Sample obtained from 3-ft vertical channel in middle of 6-ft soil exposure on roadside cut bank.

Profile S54-1 Continued

Topography. Undulating to rolling upland limestone karst

topography (alt about 200 ft). Surface gradient is about

3 percent at the sampling site. 

Vegetation. Pasture at edge of fairly large cultivated area;

contains weeds, shrubs, vines and scattered scrubby Leuceana

glauca, and some lemonchina 15 to 18 ft high.

Sample Depth Description 

S54-1-1 0-6 in. Very dark grayish brown (10YR 3/2,

dry) clay; subangular blocky, but 

coarsely granular at surface of 

soil; plastic when wet; firm when 

moist; very hard when dry; contains a few small black egg-shaped 

pellets or concretions of manganese 

(2 to 3 mm diameter); pH 6.5.

1-2 6-18 in. Mixed brown (7.5YR 4/4, moist) and 

strong brown (7.SYR 5/6, moist) 

clay; angular blocky; moderately 

plastic when wet; very firm when 

moist; very hard when dry; contains numerous root hairs and pinholes; coarse roots in upper part. 

The peds, fracture faces, and 

root channels are coated with 

dark-brown (7.SYR 3/2, moist) 

and reddish-brown (SYR 4/4, 

moist) clay. Contains many s mall 

(<1.0 mm diameter) hard to 

somewhat soft black to reddishbrown concretions; fairly porous 

when dry, with many small cracks, 

fractures, and worm or root holes; 

pH 5.5.

1-3 18-32 in. Strong brown (7.5YR 5/6 moist) 

clay; subangular blocky; firm; 

plastic; a few root hairs and some 

old root channels «l-in. diameter) filled with hard reddishbrown (SYR 4/4) clay; small soft 

black concretions occur sporadically in upper part of horizon; 

some roots about 0.25-in. diameter 

and cracks 0.25-in. wide at the 

soil surface extend down through 

this horizon; pH 6.5.

1-4 32-46 in. Similar to overlying horizon, but 

with less discoloration on fracture 

faces; fewer roots; fewer concretions (except in upper part). 

Rests on rubbly white argillaceous 

limestone at 40 to 46 in.; pH 8.0, 

measured 2 in. above limestone. 

(Sample S54-1-5, from 46 to 52 

in., is a rubbly white argillaceous 

limestone, pitted and angular, 

soft, powdery, containing numerous cavities partly filled with 

brown and strong brown clay; 

some cavities partly filled with 

limonite coatings.) (Samples collected from a 5-ft test trench.)

INDEX

[Major references are In italic]

A Page

Alexander, L. T., cited. _______________________________ F4

Alifan Limestone, average insoluble content-... _____________ _ __ 33

minerals. __ .. __________________________________ 34

Alteration of rocks of Guam, stages. _______________ .... ______ 32

Alumina accumulation, in Asan clay. _______________________ 28

inlatosols-. _____ .. ________________________ 27

Alutom Formation... _______ . __ .. _ . ___ ... ____ .... _ _. __ 2, 15,25

Mahlac Member __... ____ _ __ ______ ___ . _ . _ _ __ __ . 2

See also Asan clay.

Andesite _- __ _ .- _________ __ __ ... ___ _ ... ___ . __ 1,2 

Antrim, Northern Ireland, laterites of the Interbasaltic Horizon. ... _____ 38

Asan clay, percentage of ferric oxide.. ------ _ -.... .. __ ... 28

profile, pH_ __ -.-- __ ...-. _ .... . _____ _____ ..... __ ... 9

Titania content _ - ____ - ___ . ________ 29 

Asan clay brown re gosol on Alutom Formation.- _ .--.. _ ... __ _ ... _ . 9 

chemical constituents in soil profiles.. __ . __ . ___ ______ .. 11 

heavy minerals in sand fractions.. .-..--..-. __ .--.- ______ 14 

ion-exchange capacity. -.. .. ___________ ______ IS 

percentage of organic carbon ___ . ___________________ 1% 

profile S54-23- - . -_ ... _ ___ 12,26,27,47 

profile S54-23-1 ... . ...... .. ..................... ______ 32

silica removal. .. ______ . ________________ . _________ 27

Atate clay, on Alutom Formation, chemical composition ... __ . _ _ ... _ - JtS

on alutom formation normative clay mineral composition... .._._.._ __ 29

profile S64-4.................. ...... ................................ 9,25, 43

profile S54-5... - . --..--......-----... 9,10,12,26,43

profile S54-20. ....... ..................................... 9,^6

profile S54-21 __ . . __ . __ . __ . __ . _ ..... _ .. _ . __ .. 13, 46

on Bolanos Pyroclastic Member of Umatac Formation, profile S54-6 _ 9, 26, 27, 44

profile S54-10... _ ..--- __ .-.-.--. _ ... _ - _ ..--... __ . _ .. 9,31,45

on Facpi Volcanic Member of Umatac Formation, profile S54-12 _ 9, 13, 26, 27, 45

on volcanic rocks, average percentages of grades of silt and clay in profiles.. 7

chemical constituents _ ______ _________ ____ . __ __ 9,11

free iron oxide..-.-- _____ _ . _ ___________ ____ Q,12 

heavy minerals in sand fractions. _____________________ 14 

Ion-exchange capacity ....-- _ __________________ __ 12

minerals..-. __________ _ . ______ __________ _ .. 40 

minerals in silt and clay fractions __ __ _ __ _ ___ ...... __ . 18

percentage of organic carbon. _____________________ 12 

percentage of sand, silt, and clay in soil horizons ____________ 9 

percentage of SiOj. __________________ ___________ 9 

pH of profiles _ ___________________ . ___________ 8,9 

silica removal _ ... _____ _ _____ __ ____ __ .. ___ _ 27

profiles, silt and clay.. ______________________________ 9

Titania content- .. ______________________ . _______ 29

uniform profile ... ___ _____________ . ______ . ___ . __ 36

Atiu Island, chemical composition of red soils... ___ . _____ . ___ . __ 39

Australia, clay content of terra rossa __________________ . _____ 40

fossil laterites ___ .. ____ . _________ . ________ ____ .. 28

B

Barrigada Limestone. __ ... __ .. ___ .. _ .... _ __ ... __ . ___ ....... 40

average insoluble content __ ____ . _____ . ______ . ______ . 33

volcanic mineral assemblage... ___ _ ___ . _ __ __ .... ___ _ .. 35

Basalt flows. _______________________________________ 2,3

Antrim, Northern Ireland ____________________________ 38

Basalts, average chemical composition _____ __ . _____ ______ __ 25

Guam ____ ___________________________________ 2, 31

36

28

37

38

Bauxites, County Antrim, Ireland- ______________________ . _ 38,39

Jamaican ________ __________________ . _________ 35,39,40

Bergquist, H. R., analyst.. _____________________________ *40

Blackmon, P. D., analyst _ ____________________________ F5, 8

Hawaiian Islands.. ___ 

percentage of ferric oxide.-. 

soils developed on..-. __ __ _ 

in Lismore, New South Wales

Bramao, Luis, cited. 

Bower, C. A., cited-.

Page

20

5

Carroll, Dorothy, analyst . 12 

cited 5,15, 23, 24, 27, 33, 34, 35, 38

Chacha clay, chemical composition of profile compared with those of Guam

clays--. ... ._. 30

on Agana Argillaceous Member of Mariana Limestone, profile S54--.---. 34,49 

profile S54, free iron oxide-.---------------------------------- 12

ion-exchange capacity_____._ _ 12 

percentage of sand, silt, and clay. 9 

profileS54-l. . 34,49

on limestone, chemical constituents... 11

on Mariana Limestone, profile S54, minerals in silt and clay fractions 20

normative clay mineral composition___ .._. . 29

Chemical composition, average, soil profiles on volcanic rocks and limestones.. 25

of bauxitic soils.. . - - 39

of parent rock and soil profile, Atate clay on Alutom Formation 25,26

Atate clay on Bolanos Pyroclastic Member of the Umatac Formation.. 27

Atate clay on pillow basalt of Facpi Volcanic Member of the Umatac

Formation_-.___ __ 27 

Chemical constituents in soil profiles__. 9 

Chemical differences between soils on volcanic rocks and limestones .. 11 

Clay and silt fractions of soils, minerals 18 

Clay mineral composition of soil profiles on volcanic rocks and limestones 29 

Clay mineral development in soils associated with limestones, schematic

sequence of events 41

D

Dacites.

Dean, L. A., cited 

Deb, B. C., cited. 

Dikes.. . __ .

 2

 36

.__ 5

 2

average chemical composition__ .. %5

mafic_____________________________ 31

Dinnin, J. L., analyst.. ... 2

Dominican Republic, aluminous lateritic soil_ 39,40

aluminous lateritic soil, minerals 40

Drainage... 35

E

Elmore, P. L. D., analyst.... 7 

Eyles, V. A., cited . - 38,39

Faust, G. T., analyst-.- . ----- - - - 2,20

Fieldwork 2

Fossil laterites in Australia. 28

Fossil latosol, on Alifan Limestone profile S54-24.. 49

Fossil red latosol, chemical constituents... 11

heavy minerals in sand fractions..------ IS

minerals in clay and silt fractions. IS

normative clay mineral composition.... ---- %9

on Mariana Limestone, free iron oxide content profile S54-24 12

organic carbon, free iron oxide, and ion-exchange capacity - 1%

Q

Goldich, S. S.f analyst - - - - -- 40

Guam clay, average chemical composition.. 29

average percentages of grades of silt and clay in profiles. 7

changes in chemical composition --- 30

heavy minerals in sand fractious.. H

on limestones, chemical constituents.. 11

free iron oxide.... 1&

ion-exchange capacity. 1$

minerals in clay and silt fractions. 19

F51
F52 INDEX

Page 

Guam clay Continued

on limestones Continued

percentage of organic carton-__-_-_ -__- __________ -____ -_-_-_ F72

percentage of sand, silt, and clay in soil horizons - --_________-_.__ 9

pH of profiles.---.--------------_-_-_-_-__-_-.-._____......_,... 9

soil profiles._--.. '_-_ __--_.__--_-__--___-_---________....___. 3

on Mariana Limestone, detrital facies profile 854-17---..------------------ 48

minerals..-_---------_______ __ _. _______..______ 40

molluscan facies, profile S54-18_------_---.----______---__---____... 48

normative clay mineral composition.______._--_--____________..____._ $9

reef facies profile S54-19._---__________-..______...._-_____ 48

percentage of alumina -_------___...-___________-___._._..._._. 30

percentage of iron oxide... _.._-.--_.-.--------_-_____-.._-________ SO

percentage of phosphate. --__---__._________________________--........ 30

percentage of titania_.___-.._..___......_-__.-_-_____._.____..___-_--- 30

red latosol-__._____._____.___________._____._..__ 29,40

on Barrigada Limestone profile S54-16___-_____________-..__ 48

H 

Hathaway,!. C., cited.--------------,------._-__--__-__._.-_-__ 5,15,24,33,34,35

Hawaiian Islands, basaltic rocks ._ .._ - -_ -___ _ _ _ 24,41

volcanic rock soils-...________.___________________._ 36

Hutton, J. T., cited-------------------._-_-.--_-..---__------...-.--..-.--._. 36,37

Interpretation of thermal reactions...-.-__------------__-_-_--.

Inverell, New South Wales, profile of a laterite on basalt, descriptionion-exchange capacity, soils on limestone.-----_.._---_._-------

soils on volcanic rocks.----------________________---___.___,_.

surface soils, Guam clay.._-.--_-._...._..___.____._... 

Israel, clay content of terra rossa_____._._.-...__-_._._____

Jamaica, bauxitic soils.._-_---__--__..._...__._---...__.. 35,39,40 

principal clay minerals--------_____.-._-.____-- __........ 40

Kilmer, V. J., cited.

Laterites, Australia.._________________________________ 27,39

County Antrim, Ireland_-------_____....._-_____..-..__.._-______ 38,39

Latosols (Atate clay), percentage of ferric oxide.______._________ 28

Lava flows, basaltic___._..___-------._..........--.___......._..... 2,3

inafic_-_--_----_-__---._-______-_____-.-.--.._.-_-___.____...___...-_____- 2

Limestones, insoluble residues, variation_-_....._--.__.................. 33

mechanical composition of soils.-------------_-___.-____-------__.._ 7

minerals in insoluble residues..------__-----__--.__............... 34

normative clay mineral composition of profiles._ _________._.___. 89 

organic carbon in soils._- ________ _ ___ ___ _ ___________ ___ 19

red soils associated with, occurrence- _------___-_-----_---_._._... 39

Lismore, New South Wales, soils developed on basalt___-------_------- 38

M 

Mclntyre, D. S., cited--____________________________.....

Mangaia Island, chemical composition of red soils __..-.---. _.......... _..

Mariana Limestone.-____________________.________ 2,9,12,

Agana Argillaceous Member...._-___.___-----_._____-.-..---. 

clay derived from weathering of volcanic rocks_..--__________.__

average insoluble content..__._.--__._____.._-----------_.__..___.

volcanic mineral assemblage.--------__-__...-__._-.-...-.......

See also, Chacha clay. 

Marshall, Patrick, cited.______________..._______._____._...

Methods of examination of soils of Guam....______. _____.__.__._._.__

Mineral composition, changes.----------___....____....._-----

Minerals, alpha-cristobalite-----------_-_-_--_..._-____--_---------___---

amphiboles----..----_..-..--_..._......._..............._....-_- 13, IB, 28,

anatase_------___._..._______..._._-----------_-.._. 18,

augite...-.....---_.-_....-. ...-----...-.------.------------------- 3,13,

biotite_-___..---...___---..._____.______.__...._...

boehmite_________________________________ 20,23,34,

calcite_________.________________....................

celadonite.--.-.-..--.-.............-__._....__._.--.._...__._..._..__.__.

chlorites..................................................................

chromite--. ___.....____.....___...__.-.._...__....

day................................................................. 3,29,

endellite.......

epidote........

feldspar. .... 

alkalic..... 

plagioclase.

30

39

40,41

24

40

33

35

39

4

32

20

33,34

20,32

IS, 34

3

35,41

3,35

3,32

3

20

40,41

32

3

32,34

3

3,33

Page 

Minerals Continued

gibbsite ___-__-_ -----_--____---_-_ ___- F20,23, 29,32,34,35, 36,40, 41

goethite ____________--.--___-__-_____-..--.---__..__.-___-_-____ 11,15,23,28,32

halloysite - - - - - - - 20,23,24,29,32,36,40,41 

hematite _... .......... -- .... - 11,15,20,23,28,29,32

hornblende.-.-_--__--_-_-_--_---------.--__--__.--- -.._.___-- _--- 3

hypersthene_________..__.________..-_______.______ 3,13, IS, 34

ilmenite.______-__-__-_________________________ 13, 15,34 

in heavy residues------ --_.------____-___------. --_-_.__--_------ IS

in volcanic rocks_--.____-.._-_____-_________-------__----- ._ _..- 3,31

in weathered rocks __ . . __- _.-- ------- 31

Jamaica bauxite. __- ._-___- ___. ------ ____.._-__ - 40

kaolinite._-__ _--------------------_--------_----------------------------- 20

lateritic soils..--...______-...__..__..._...______---- 40

magnetite-- IS, 15, 20,31,34

montmorillonite ... 20,23,32,35,36

montmorillonite-halloysite, mixed layered...---... ...- - --.. 19,20,23,32 

nordstrandite._-... - --------------- -------. .- ----- 35

olivine -_. -------------- ------. -- -... 3

plagioclase..--------- - - ------------ ----- 32

pyroxenes.--.-_ _.--- _ _____ .--_ ----- -------- 3,28,33

quartz----. 3,20,33,34

rutile........... 13,15,32

saponite.------------ - -------------- . ------. -. 32

sericite. . 32

serpentines..-- .. ----- ----------- - --- - 3

silica, opaline..-------------- ------- . -- ----- 3

sphene----------- --------------------- ----- ----- ---- 13,15

weddelite_-____--_- ____ ------- -------- ---------- 20

zeolites...-. ----------- . ------ -- 3,32

zircon ------ _-_ - ------------- ------ ... 13,15

Mohr, E. C. J., cited 15

Mount Lamlam, mineral content of soil ..-. .... 34,41

N 

Nicolls, K. D., cited 32,38

Norfolk Island, south Pacific Ocean, volcanic rock soils. _ 36

Norrish, Keith, cited 38

O 

Organic carbon of soils, on limestone ---------- ------ ------------ IS, 13

on volcanic rocks. ------------------------------------------------------ 1%, 13

P

pH of soils, Lismore, New South Wales.. ----------------------------------- 38

Norfolk Island, south Pacific Ocean.------ _- -__ _-_- 36

on limestones.-----.-----.-----. -. .--- ..--- -------------- 7,9,34

on volcanic rocks...- - -------- __. ----------- - --------- 7,9,34

Phillips, H. F., analyst 2> ?

Profiles, pozolic ------------ ------- -_-.. ._-- - - 36,38,39

uniform...._---_-_._.. - . -- 36,41

R

Reiche, Parry, cited.. - 31 

Residual red latosols .... 1.3

Saipan clay . - - ------- -------- ------- - 

Sand fractions of soils, minerals --------------- - ----------------------

Saprolite.--------------------------------------------------------------------

Scott, P. W., analyst------------------------------------------

Shales, marine tuffaceous.------------------ ----------------------------------

Silica removal, Asan brown regosol on Alutom Formation.--- ------- 

in latosols (Atate clay) _ - - --- ----- -----

soils on limestones.-.-- - ----- - ----------- - -----

Soil horizons, variations in amounts of silt and clay.___- -------- 

Soil profiles, description.--------- - - ------------------ ---------

Hawaiian Islands__- ------ ----- - -- ---

on limestone - ------- -- - - -------

average chemical composition- -_-.. ..-_--- ------

on volcanic rocks.--- ------------- -- - --------

average chemical composition - - --- - - -- -- 

organic carbon in surface samples, percentage. - ------------ 5

Soils, developed on basalt . -- ----------- ---------- - 

developed on volcanic ash._._. ... ---------

Krasnozems..- ... ------ -------

minerals.. - - - -- --------------

sand grades ._ . ....... --- --

silt and clay grades. 

onlimestone, description of soil profiles ... - ----

free iron oxide.. - - ---- --

ion-exchange capacity-- 

3

13

32,40 

2

2,3 

27 

27 

29 

9 

43 

36

1,3,4 

25

1,3,4 

25

12, IS 

37 

37

36,38

31

5,37

5

48 

12 

12
INDEX F53

	Page 

Soils Continued

on limestone Continued

major chemical constituents,-------- __-__-,____-_._____-__-__-_ F10

mechanical composition 8

mineralogic composition...------. ------------------------------ 32

organic carbon. --------- ---- ------------------------------- 12

percentage of silt and clay..------------------------------------------ 13

pH - - 10

principal soil type..---. --.. ----------- ..-- ._-._. 29

on limestones and volcanic rocks, difference between._- - _ -- 29

on volcanic rocks, description of soil profiles------------------------------ 43

free iron oxide.------ -------------------------- .____-_- 12

ion-exchange capacity------------ --_-_- -_.-----_ .--. . 12

major chemical constituents..._-- --------------------------------- 10

mechanical composition _--_- - .._ -___-__-- _ _ . 8

organic carbons ----------------------------------------------------- 12

percentage of silt and clay...... .. 13

pH. - - 10

silt and clay grades. .. - .- - 5

upland limestone, description .-.. -------. ... ------------ 3

upland volcanic, description -------- _ _ _---- _-- 3

Soils and volcanic parent rocks, relationship between.-.____. _-__ ..._ 24

Stark, J.T., cited . 2,3

Starkey, H. C., analyst - -- - 12

Stephens, C. G., cited.. 36,37

Surface soils, Guam clay, ion-exchange capacity . 13

Terra rossa, inlimestone areas - - . ...-. -. 29

Israel, clay content. - --- 40

red soils associated with limestones, occurrence---- - 1,29,39

Terra rossa deposits, Mediterranean regions.---------- .. ------------ 1,29

Terra rossa type of bauxites, occurrence ------ -------. . 39,41

Terra rossa soils, free iron oxide ----- -. . ---------- 30

Thomasi, E. J., analyst . -- 7 

Titania in volcanic rocks..-.. 28 

Totoclay - - - - - - --- 3

Tucker, B. M., cited..- . 32,38

Trumbull, L. D., analyst_ ... - - 7 

Truog, Emil, cited.. -------------- 5

Page 

TuflEs-- - .. F31

average chemical composition-..__.....__...____.___...._.. 25 

percentage of ferric oxide._....__-.._---.._..._-...._.._-.-._-...... 28

U

Umatac Formation, Bolanos Pyroclastic Member......______._____ 2,13,

Dandan Flow Member..-..._...-._-..._.__._ ______._-.. 2

Facpi Volcanic Member _._----------_. _ ______......._. 2

See also Atate clay. 

Maemong Limestone Member_---------------__-------___._... 2

van Baren, F. A., cited.-._____________________________ 15 

Volcanic ash, minerals_-___-_.-..___-..-______.._._-. 33,35,39

soils. .-----.--.---- ----- -------------_______--.-. 37

Volcanic ash falls______.________________..______.. 2,35,41 

Volcanic glass....____.-..__..______......__...-___..._- 28

Volcanic rocks, average chemical composition_-------___-.-.----.-----__ 25

mechanical comiposition of soils. ---- - - --- - _-..-----.-------. 7

normative clay mineral composition of soil profiles. _ _.-__ _ ___ 29 

organic carbon in soils....- ----------. ----------. .__._ 12

percentage of ferric oxide. ----------- ------- ---------------------- 28

percentage of titania -.-- -------- - _--._ _.__.. 28

principal minerals._....--.. ... - . .... 3,31,33

weathering...______----- ------- ..-_------___ 3,31,40,41

W

Water, quantity in soils on volcanic rocks and limestone. _ -.. _._ 29 

Weathering Potential Index..-. 31

Weathering process in development of Atate clay, principal.._ -__ __.__ 27 

Weathering processes, effect on rocks.._. _ _ ------------------ 3,31,40,41

White, K. E., analyst-.--------------------------------------------------- 7

Woof, Marion, cited_____ - ... _ 27,38

Yona clay.

Zans, V. A., cited ---- - 35,40

U. S. GOVERNMENT PRINTING OFFICE : 1963 O - 677 - 184