Elsevier Encyclopedia of Geology

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Micaceous clay minerals in soils are mostly rock-

derived and comprise both clay-grade micas and true

illite. However, illite-rich illite-smectite can form

through K fixation in smectite (especially high charge

smectite) in soils subjected to repeated wetting and

drying. Most soil illites, whatever their origin, are dioc-

tahedral aluminium-rich illite. Smectite formation

(Figure 4) is favoured by high pH, high silica activity,

and an abundance of basic cations, consequently smec-

tite is associated with poorly drained soils on base-rich

parent material. Smectite formed in this way may

be mostly ferruginous beidellites. However, smectites

can form through transformation and neoformation in

a wide range of soil types. The situation is further

complicated by the frequent alteration of volcanic ash

to form smectite (usually montmorillonite), which can

occur dispersed through sediment or as discrete ben-

tonite layers (see Sedimentary Rocks: Clays and Their

Diagenesis).

Most soil vermiculite is trioctahedral and forms

through weathering of biotite, hence many soil ver-

miculites are interstratified illite-vermiculite (called

hydrobiotite when regularly interstratified). Vermicu-

lite can also form from chlorite through breakdown

of the interlayer hydroxide sheet, though again, the

mixed layer clay is most frequently encountered in

soils (vermiculite-chlorite is also known as swelling

chlorite). Dioctahedral vermiculite is also present in

soils but is less well known.

Most trioctahedral chlorite in soils is inherited.

Primary chlorites are easily weathered to chlorite-

vermiculite, or if weathering is intense, dissolved al-

together. This is why chlorite is characteristic of high

latitude soils where surface weathering is less intense

than anywhere else on the Earth. So-called pedogenic

chlorite and chlorite-rich interlayered clays appar-

ently form entirely through transformation reactions

involving the introduction of nonexchangeable inter-

layer hydroxy-Al polymers into the interlamellar sites

of pre-existing smectite, and vermiculite or interstra-

tified expandable clays. This transformation is

favoured by pH 4–5.8, and it appears that in podzols

at least, the reaction may neutralise acid rain.

Neoformed kaolinite is associated with tropical

soils, particularly on stable cratonic areas. The reason

for this association is that the intensity of weathering to

form kaolinite from rock is greater than for other clays.

Kaolinite formed through transformation reactions is

less common but the existence of kaolinite interstrati-

fied with other clays suggests that these reactions do

occur. Soil-formed kaolinite differs from diagenetic

kaolinite in having some Fe substitution for Al, being

less well ordered, and having a smaller particle size.

Neoformed kaolinite (Figure 4)isalsoassociatedwith

limestone karst formation (see Sedimentary Processes:

Karst and Palaeokarst). Commercial deposits of kao-

linite (china clay) have formed through metasomatic

alteration of granite (see Clays, Economic Uses). These

are almost pure kaolinite and contain only minor

quartz impurities. Kaolinite-rich beds known as under-

clays, tonsteins, or seat-earths occur beneath coal de-

posits, where they form as a consequence of intense

plant-assisted weathering. Dickite is typically a high

temperature diagenetic clay, while both dickite and

nacrite are associated with hydrothermal deposits. Hal-

loysite is mostly associated with young, volcanic-

derived soils, in which it has a characteristic tubular

or spherical morphology.

Interstratified clays are very commonly neoformed

in soils. This is because the represent intermedi-

ate transformation products in reactions which

proceed less fast at the Earth’s surface than in

during buried diagenesis. Various mica-vermiculites

and illite-vermiculite are common in podzols, while

Figure 4 Pathways for the formation of clay minerals in soils.

Most smectite and kaolinite is formed through neoformation

while formation of kaolinite from mica and chlorite is not a true

transformation due to the structural differences. (Adapted from

Wilson (1999).)

CLAY MINERALS 363

chlorite-vermiculite is found in a wide range of soil

types on chlorite-bearing rock. Kaolinite-smectite (or

more probably the kaolin mineral is halloysite, though

this has only recently been recognized) is particularly

abundant in soils formed on basic igneous rock.

Globally sepiolite and palygorskite are fairly rare

though locally abundant. Recent and Quaternary de-

posits occur in North Africa and the Middle East,

while there are well-known older Tertiary deposits in

southern Spain and France. Neoformed sepiolite and

palygorskite are commonly found in desert soils,

ephemeral lakes, and playas, and occasionally in hy-

drothermal veins in basic and ultrabasic rocks. For-

mation of palygorskite requires confined conditions,

either in shallow, enclosed water bodies at times of

low lake level or in palaeosols and slow deposition. It

occurs in mature, slow-formed calcrete, and in associ-

ation with smectite and dolomite. Palygorskite does

occur in deep water sediments. For example, the

origin of palygorskite in deepwater sediments of the

North Atlantic has been much debated. However,

using SEM and TEM analysis, this clay has been dem-

onstrated to be wind blown, reworked material from

shallow water saline basins in Morocco.

Marine Clays

The clay mineral suite of marine environments is

controlled by provenance (closely linked to climate),

salinity, particle size, and neoformation. Detrital clay

minerals distributions in estuaries and deltas reflect

the different settling rates of the clays present and

their tendency to flocculate. Where flocculation does

not occur, the finer clay particles (which roughly

equates with smectite) remain in suspension longest

and are transported further offshore. However, no

such depth profile will occur if mixing of freshwater

suspended clay with saline water results in floccula-

tion, or where marine currents are strong. The effect-

ive grain-size of clay particles is also dramatically

increased through the formation of mucous-bound

faecal pellets by marine invertebrates. Due to the in-

corporation of reactive organic matter into faecal

pellets, they are prone to allogenic and early diage-

netic mineralisation. An example is odinite, a ferric

iron-rich clay that forms exclusively within the

tropics, offshore from major river systems (which

introduce large amounts of iron into the marine envir-

onment). Odinite replaces faecal pellets and also

forms ooidal coatings on grains. In ancient sediments,

odinite is believed to transform into ferrous iron-rich

(berthierine) and 14A

(chamosite) clays. Further

offshore in marine shelf sediments, the better known

iron-rich clay, glauconite (and intermediate clays

which range from glauconitic smectite to smectitic

glauconite) forms just below the sediment water inter-

face, again, largely through replacement of faecal

pellets. Glauconite forms principally on the outer

shelf, in a water depth of 100–300 m, at a temperature

of 7–15



C and between 50



Nand50



S. It is also

favoured by a low sedimentation rate because it is

slow to form and has an He close to the redox bound-

ary as it contains both ferrous and ferric iron. Hence

glauconite is associated with transgressive sediments,

and can be a useful environmental indicator, though

there are many instances of reworked glauconite in

turbidites, shallow marine, and nonmarine sediments.

Deep sea clays cover by far the greatest area, but are

deposited very slowly. Much of the clay in these sedi-

ments is a combination of detrital and neoformed Fe-

rich smectite, often associated with palygorskite

(which may or may not be authigenic) and authigenic

clinoptilolite. In the central Pacific, where there is

perhaps the least detrital input, smectite makes up

>70% of the clay fraction. Nontronite has been

reported from deepsea areas of volcanic activity.

Apart from neoformation of smectite, the deep ocean

clays largely reflect the pedogenic processes occurring

on adjacent landmasses.

Nonmarine Clays

Most continental, freshwater, and saline lacustrine

clays are detrital. A few recent saline lakes contain

unequivocal neoformed Fe and Mg-rich smectite.

However, studies of lake clays do not always include

sufficient investigation of the drainage basin to be

certain that just because a lake clay is dominated by

one clay type that it is neoformed. Some Tertiary lake

sediments are almost monomineralic ferric rich illite,

but the same provision regarding the drainage basin

applies to these. There appear to be two distinct

processes whereby this unusual clay forms, firstly

in volcanic lakes with a high dissolved cation content,

and secondly in ephemeral lakes through repeated

wetting and drying of smectite. Laboratory experi-

ments have demonstrated that such a process is

possible.

Clay Stratigraphy

As a consequence of diagenetic replacement by illite,

smectite is virtually unknown from pre-Mesozoic

sediments, while throughout the Mesozoic and Early

Tertiary, smectite is the principal clay mineral found

in sediments of most types. Glauconite is most

abundant at the end of the Cambrian and the end of

the Cretaceous, while berthierine/chamosite are

mostly found from the Ordovician to the end of the

Devonian and from the earliest Jurassic until the end

364 CLAY MINERALS

of the Cretaceous. The reasons for these particular

distributions through time may be related to the avail-

ability of suitable formation sites, which may in turn

be linked to global climate and the formation/break

up of the supercontinents. Global climatic shifts, es-

pecially in Tertiary and more recent sediments are

clearly reflected in the clay minerals formed at the

Earth’s surface and consequently deposited in the

oceans. The global cooling that began at the Eocene–

Oligocene boundary and continued intermittently is

reflected in the shift from a predominance of smectite

to illite, plus minor chlorite and interstratified

clays. At the same time, falling sea-level associated

with global cooling and the build-up in polar ice

resulted in the spread of nonmarine basins, hence

the widespread freshwater clay deposits of the Oligo-

cene. Recent research into clay stratigraphy is begin-

ning to show that where post-formation modification

is absent, clay mineral suites can accurately reflect

Milankovitch cyclicity in sediments, and hence

provide a geologically fine-scale dating tool.

Changes across stratigraphic boundaries, particu-

larly where they are nonconformable, are not uncom-

mon, and can be useful for dating purposes in

nonmarine sediments, while within a single sediment-

ary unit, clear vertical changes in clay mineral suites

in marine shales can be demonstrated to be linked to

changes in ocean circulation and faunal changes.

Note that lateral facies variations can result in lateral

clay mineral suite variation, even within shales, and

care should be taken when attempting to use clay

stratigraphy in this way, especially if the intensity

of diagenetic alteration varies between locations (see

Sequence Stratigraphy).

Further Reading

Aplin AC, Fleet AJ, and MacQuaker JHS (1999) Muds and

mudstones: physical and fluid-flow properties. In: Aplin

AC, Fleet AJ, and MacQuaker JHS (eds.) Muds

and Mudstones: Physical and Fluid-Flow Properties,

Special Publications: 158, pp. 1–8. London: Geological

Society.

Bailey SW (1980) Structures of Layer Silicates. In: Brindley

GW and Brown G (eds.) Crystal Structures of Clay

Minerals and their X-ray Identification, Mineralogical

Society Monograph No. 5, pp. 1–124. London: Mineral-

ogical Society.

Chamley H (1989) Clay Sedimentology. Berlin: Springer-

Verlag.

Colson J, Cojan I, and Thiry M (1998) A hydrogeological

model for palygorskite formation in the Danian contin-

ental facies of the Provence Basin (France). Clay Minerals

33: 333–347.

Huggett JM (1992) Petrography, mineralogy and dia-

genesis of overpressured Tertiary and Late Cretaceous

mudrocks from the East Shetland Basin. Clay Minerals

27: 487–506.

Huggett JM, Gale AS, and Clauer N (2001) The nature and

origin of non-marine 10A

green clays from the late

Eocene and Oligocene of the Isle of Wight (Hampshire

basin), UK. Clay Minerals 36: 447–464.

Moore DM and Reynolds RC (1997) X-ray Diffraction and

the Identification and Analysis of Clay Minerals. Oxford:

Oxford University Press.

Merriman RJ (2002) Contrasting clay mineral assemblages

in British Lower Palaeozoic slate belts: the influence of

geotectonic setting. Clay Minerals 37: 207–219.

Robert C and Chamley H (1992) Late Eocene-Early

Oligocene evolution of climate and marine circulation:

deep-sea clay mineral evidence. The Antarctic Paleoen-

vironment: A Perspective of Global Change Antarctic

Research Series 56: 97–117.

Rupert JP, Granquist WT, and Pinnavaia TJ (1987) Cata-

lytic properties of Clay Minerals. In: Newman ACD (ed.)

Chemistry of Clays and Clay Minerals, Mineralogical

Society Monograph No. 6: pp. 275–318. London:

Mineralogical Society.

Srodon J (2002) Quantitative mineralogy of sedimentary

rocks with emphasis on clays and with applications to

K-Ar dating. Mineralogical Magazine 66: 677–688.

Velde B (1992) Introduction to Clay Minerals. London:

Chapman & Hall.

Vogt C, Lauterjung J, and Fischer RX (2002) Investigat-

ion of the clay fraction (<2 mm) of the Clay Minerals

Society reference clays. Clays and Clay Minerals 50:

388–400.

Wilson MJ (1999) The origin and formation of clay min-

erals in soils: past, present and future perspectives. Clay

Minerals 34: 7–26.

CLAY MINERALS 365

a0005 CLAYS, ECONOMIC USES

Y Fuchs, Universite

Marne la Valle

e, France

Introduction

In common parlance, ‘clays’ are aggregates of min-

erals, soils, or rocks that commonly show plasticity.

These materials contain not only minerals belonging

to the clay family (see Clay Minerals) but also very

fine particles with various proportions of quartz, feld-

spar, mica, and organic material. Clays are estimated

to represent about 15% of the volume of Earth’s crust

as soils and as sedimentary rocks (mudstones, shales).

In soils, clays play a major role in moisture retention,

permeability, and adsorption of inorganic (metals)

and organic solutes, as well as in the propensity for

soils to shrink and swell. Thus the presence of clay

minerals in soils is important for agriculture and con-

struction. Clay has many other uses, however, and it

is a particularly important commodity for industry.

According to the United States Geological Survey, in

1998 there were approximately 770 active open-pit

clay mines in 44 states of the USA. These mines, oper-

ated by 240 companies that employed 13 700

people in clay mining and milling, sold 43 million

metric tons of clay products, with sales averaging

$2.14 billion year

1

History

Clays have long been and are still used in different

processes and products, from traditional house build-

ing (adobe in Latin America and toub in Africa, when

mixed with straw) to personal-use products (sham-

poo, or ‘rassoul’, in North Africa); in ad 77, Pliny the

Elder mentioned clays used as ‘soap’. Advanced tech-

niques now allow use of clays in the production of

resistant, high-temperature ceramics and in remedia-

tion material and water-circulation barriers for waste

repositories. Clay has been used as the building ma-

terial of choice for millennia. Sun-dried bricks

(adobe) and kiln-fired bricks were employed by

the Sumerian and Babylonian civilizations of the

Euphrates region for constructing ziggurats, city

walls, palaces, and temples.

Clays have played an important role in pottery

and vessel manufacture and in the trade in such

goods. The earliest forms of clay pottery are about

10 000 years old. Stoneware items incorporating clays

dating from 3400 years ago have been discovered in

China. The oldest porcelain known was created in

China during the Tang dynasty (ad 618–907). The

import and trade of Chinese porcelain in Europe

were important for centuries, and porcelain remained

a very expensive product until it became more widely

available in Florence at the end of sixteenth century.

Definitions

The term ‘clay’ has somewhat different meanings

in different contexts (Figure 1). To the mineralogist,

‘clay’ is the term describing a mineral family charac-

terized by its crystal structure. To the geologist, ‘clay’

designates a type of rock in which clay minerals are

particularly abundant but in which other minerals,

such as calcite and quartz, also contribute to the rock

composition. For industrial purposes, the definition

of ‘clay’ is based on grain size (typically <2 mmin

diameter). The importance of clays and clay minerals

in economic geology derives from their fine grain size,

their chemical composition, their layered structure,

and the characteristics related to theses physical at-

tributes, i.e., their role in ion exchange and their affin-

ity for water. The importance of clays in economic

geology is large and varied.

Industrial names of clay types do not correspond to

the names as they are defined by the International

Mineralogical Association (IMA) and as they are de-

fined by researchers. Industrial names are generally

based on the six categories established by the US

Bureau of Mines: kaolin, ball clay, fire clay, bentonite,

fuller’s earth, and so-called common clay and shales.

Kaolin, also called china clay, is composed mainly of

kaolinite and other kaolinite group minerals (nacrite,

halloysite, and dickite) and must be white for indus-

trial uses (e.g., paper coating and filling, refractories,

rubber, and paint). Ball clay is plastic, white-firing

clay containing mainly kaolinite. It is used for manu-

facturing tiles, dinnerware, and bath and kitchen

sinks and tubs. Fire clays withstand temperatures up

to 1500



C and are used for refractories or to raise the

vitrification limit. They are also composed mainly of

kaolinite but may also include diaspore, an alumin-

ium hydroxide (a-AlO(OH)), burley, ball clay, and

common clay. Bentonite is an industrial clay that is

composed mainly of clay minerals from the smectite

group and principally of montmorillonite; it is used in

foundry sands and as drilling muds. Fuller’s earth is a

non-plastic clay material that is characterized by its

particular purifying and decolourizing properties.

Fuller’s earth is not very different from bentonite

366 CLAYS, ECONOMIC USES

and is used mainly as pet litter and as an absorbent for

oil and grease. Common clay is defined industrially as

material that has a vitrification point below 1100



It consists of mixtures of different clay minerals,

mainly illite and chlorite, but may also contain

kaolinite and montmorillonite.

Civil Engineering

Volume changes in clay cause swelling and/or shrink-

ing of soils, a major geological hazard for buildings

and road pavement. Shrinkable clays are usually de-

posited as sediments in marine or brackish environ-

ments. They show little tendency to expand unless

they have previously undergone a strong drying

event. The shrinkage problems associated with this

type of clay in soils are related to water uptake by

deep tree roots, particularly in areas where the clay

content exceeds 25%, the plasticity index is higher

than 30%, and the water table is relatively deep

seated. Expandable clays are characterized by their

relatively high content of the clay mineral montmor-

illonite (and some other structurally related clay min-

erals of less importance). From an initial dry state,

because of their montmorillonite content, these clays

react to increasing moisture conditions by swelling.

The same clays can show a reverse shrink–swell

capacity with changed environment.

The presence of clays in soils is a problem for

foundations of even small buildings. In all countries,

structural foundations have to meet minimum re-

quirements of building regulations. Under a building,

the mass of soil that is appreciably affected by mois-

ture content change is termed the ‘active zone’. This

zone represents the volume of soil that is influenced

by the presence of an engineered structure. The

impact can be related directly to the building (heat

flow) or to other factors, such as changes caused by

vegetation (effects of tree roots). In some countries,

the depth of frost action is an important concern,

particularly for structures that do not lose appreciable

heat to the subsoil.

Building Material

Clay is a vital component in the manufacture of cements

and bricks. To obtain a valuable clinker (a name for the

material produced in the first stage of the cement manu-

facturing (after furnace)), the chemical composition of

the raw material must be within defined limits. CaO is

the most important component (from 60 to 69% in

weight content), but the crude mix must also contain

SiO

(18–24%), Al

(4–8%), Fe

(1–8%), and

minor components such as MgO, K

,andNa

The four principal oxides (CaO, SiO

,Al

,and

) are absolutely necessary. Clays extracted from

aquarryhavevariableconcentrationsoftheseoxides

and therefore it may be necessary to add material to

obtain the required composition. Limestone is the main

source of CaO. Clay or shale will provide most of the

SiO

,Al

, and Fe

A typical cement raw mix comprises around

80–90% limestone and 10–15% clay or shale.

According to the United States Geological Survey, the

production of cement in the United States in the year

2000 reached 90.6 million metric tons. These data in-

dicate that the cement industry was the most important

consumer of clay in the United States, requiring about

25% of the domestic clay production (total, 40.8 mil-

lion metric tons). Transport of huge quantities of

Figure 1 Uses of clays.

CLAYS, ECONOMIC USES 367

low-price raw material is not economical, thus the

cement industry is best located near regions where geo-

logical conditions support mining of limestone and

clay deposits.

Waste Disposal

Clay is used in containment systems for landfill

waste deposits to control the water fluxes in and out

of the system. For this purpose, industrial designers

have developed a composite material that imposes

a hydraulic constraint on the clay liner. The liner is

composed of a layer of montmorillonitic clay (normally

sodium ‘bentonite’) sandwiched between two non-

woven geotextiles or bonded to a geomembrane. The

thickness of the clay liner is typically about 6 mm. It

has the ability to self-repair if damaged; it is equivalent

to many metres of compacted clay and is not associated

with problems of moisture, drying, or tree roots that

normally affect compacted clay barriers.

Ceramics Industry

The ceramics industry uses clay in the manufacture of

bricks, ceramics (generic), glass, heavy clay products,

aggregates, tiles, and refractory products; these ac-

counted for two-thirds of the total clay production

in the United States in 1985 (total, 45 million short

tons). The most important clay mineral for ceramics

is kaolinite, Al

(OH)

. The basic chemical

principle utilized by the ceramics industry is based

on the structural and chemical transformation of

clay minerals into minerals of the spinel type. In

these reactions, kaolinite, heated at 550



C, loses

its (OH) groups (dehydroxylation process) and is

transformed into a product called metakaolinite,

, with formation of two molecules of H

At approximately 980



C, metakaolinite transforms

into a silicon spinel, 2Al

 3SiO

þ SiO

. This

phase is rather complex and probably depends on

the nature and ordering of the original clay mineral.

At 1100



C, mullite, 2(Al

 SiO

), begins to form

in association with quartz (SiO

). The reaction

continues, and at about 1400



C all the material has

been converted to mullite and cristobalite (a high-

temperature form of SiO

). Pure mullite would be

stable up to 1850



C, but the presence of SiO

gen-

erates a liquid phase at about 1590



C that can induce

silica exsolution in the material, and therefore the pro-

cess is stopped at about 1650



C. At 1850



C, mullite

would transform into corundum and a liquid-phase

SiO

. Ceramic mullite composition varies from

3Al

 2SiO

to 2Al

 SiO

, with possible partial

substitution of Al by Fe: 3(Al

0.9

0.1

)

 2SiO

.The

general process of ceramics formation at increasing

temperature consists of going from an exsolution of

silica from a primary raw material containing approxi-

mately 40% Al

, to mullite with an Al

content

up to 73%.

Refractory ceramics must have a particularly high

alumina content. The phase line diagram of SiO

–

has its highest point theoretically at 100%

and 2020



C, thus minerals such as bauxite,

with higher Al

content than kaolinite has, are

added to natural kaolin to obtain the most refract-

ory products. Earthenware, wall tile, sanitary ware,

stoneware porcelain, and electrical porcelain are

manufactured using kaolinite or ball clay, quartz,

and fluxes. One of the most important requirements

is that the product must be white or ivory in colour.

Temperatures between 1150 and 1250



C are used for

vitrification except for electrical porcelain, for which

it is necessary to reach 1400



C. Because of its colours

and its workability, kaolin is the main clay used, and

the composition of various products ranges from

100% kaolinite for porcelain to 20–30% kaolinite

for sanitary ware.

New applications for ceramics are under develop-

ment, particularly as monolithic catalyst carriers for

standard emission control equipment on vehicles. The

ceramic for this purpose has a cordierite composition

(2MgO  2Al

 5SiO

), obtained by firing a mix-

ture of 70% talc and 30% kaolinite at 1400



Ceramic membranes are another new technology.

These membranes are high-temperature (up to

1000



C) and corrosion-resistant materials that with-

stand the effects of corrosive products. They are used

in many different processes, such as beer filtration

and hot metal separation. The market for these pro-

ducts is steadily growing. Other applications for

ceramics in modern industrial processes include

permanent foundry moulds and heat exchangers.

Physicochemical Properties of

Clay Minerals

The physicochemical properties of clay minerals are

strongly related to their structures and compositions,

thus it is possible to organize them into three basic

categories: the kaolinite group, the smectites group,

and palygorskite (attapulgite) and sepiolite.

Kaolinite is a two-layer clay. Substitution of Al for

Si in the SiO

tetrahedron (Tschermak substitution) is

limited, i.e., the charge on the kaolinite layer is

limited. Because of this limited charge, kaolinite has

a low exchange capacity, particularly regarding other

clay minerals (smectites, bentonite, etc.). Related to

the low surface charge, kaolinite has low absorption

and adsorption capacities. Kaolinite is a hydrated

aluminous silicate with very limited substitutions

368 CLAYS, ECONOMIC USES

(particularly by Fe) and is therefore white in colour.

Particle size is very fine. Kaolinite is normally well

crystallized, with broad dimensional distribution and

low surface charge. These characteristics induce good

flow properties and low viscosity even at high solid

contents in water. Kaolinite is hydrophilic and will

disperse easily in water with addition of a small

quantity of dispersant. This quality makes kaolin an

essential component in paper coating and in water-

based interior paints. The paper industry is by far the

largest user of kaolin. Coating paper with kaolin

improves the printability of paper by making the

paper surface smoother, more homogeneous, and

more finely porous. To coat paper, a high-concentra-

tion solid/liquid suspension of pigment and binder is

applied to the paper surface with a blade. Differently

processed kaolinitic products must be further prepared

for rotogravure and offset printing processes. Kaolin

is also used as a filler during paper manufacture to

enhance paper opacity and strength.

Smectites are a group of clay minerals character-

ized by their three-layered structure and their chemis-

try, consisting of sodium, calcium, magnesium, or

lithium aluminium silicates. Chemical variations of

smectite minerals include sodium montmorillonite,

calcium montmorillonite, saponite, nontronite, and

hectorite. Bentonites are types of sodium and calcium

montmorillonites derived from alterations of volcanic

glasses (usually volcanic ashes) and are of great in-

dustrial and economic importance. The three-layer

structure of the smectites is very important; a single

octahedral sheet is sandwiched between two tetra-

hedral sheets. In the octahedral sheet, Fe

2þ

(ferrous

iron) and/or Mg

2þ

substitutes for Al

3þ

, creating

charge deficiencies in the layers. The charge balance

is also affected by Al substituting for Si in the tetrahe-

dral sites. These deficiencies are charge balanced by

exchangeable cations (Na

,Ca

2þ

) located in inter-

layer positions. Two or four OH groups are associ-

ated with the exchangeable cations in the interlayer

sites. The cations and OH groups located in the inter-

layer can be exchanged with other cations and also

with polar organic molecules such as ethylene glycol,

quaternary amines, and (poly)alcohols. Smectites are

generally present in nature as very small particles and

therefore they have a high specific surface. In as-

sociation with a high charge, this induces a high

degree of viscosity when smectites are mixed with

water. High cationic exchange capacity and a high

degree of viscosity when associated with water are

the properties that determine the industrial uses of

smectites.

The most important industrial user of smectites is

the oil industry. Bentonite is used as drilling mud. Its

excellent swelling capacity and high viscosity enhance

the stabilizing effect of freshwater drilling mud. Ben-

tonite mixed with sand of high silica content is also

used in foundries. Adding a small quantity of water

yields a plastic material that can be moulded. Bento-

nites are also used to pelletize iron ore and as sealants

for water ponds, ditches, and household basement

walls. Sodium bentonite can be produced from cal-

cium bentonite by the addition of soda ash. In the

presence of a soluble sodium salt, Na substitutes for

Ca in the structure. These artificial bentonites, called

sodium-activated bentonites, have better swelling and

gelling properties than the natural ones have. Indus-

trial products are frequently a mixture of natural and

activated Na-bentonites.

Palygorskite (attapulgite) and sepiolite are hy-

drated magnesium aluminium silicates. Structurally,

double silica tetrahedron chains are linked together

through chain-like structures formed of oxygen and

OH groups, forming octahedra in which the cationic

site is occupied by aluminium or magnesium ions.

Palygorskite and sepiolite are seen as fibres in scan-

ning electron microscopy. This morphology is the

result of the predominantly chain-like structure. Sub-

stitutions in the octahedral layer induce a moderate

charge in the structure, and the exchange capacity is

intermediate between that of kaolinite and smectite

(40 meq per 100 g for palygorskite–sepiolite and

60–100 meq per 100 g for smectites). The combin-

ation in palygorskite–sepiolite of particle charge,

channel structure, and large surface area results in

a high absorption and adsorption capacity that

has many industrial applications. The high and very

stable viscosity makes these clay minerals useful in

saltwater drilling mud or high-electrolyte-content

drilling mud. They are currently used in drilling

in oilfields where brines are normally associated

with oil.

In agriculture, palygorskite and sepiolite are used

as retardants in fertilizers, pesticides, and herbicides.

When mixed with these products, the high adsorp-

tion and absorption properties of the silicates allow

slow and progressive product release; this is both

economical and environmentally beneficial. Palygors-

kite and sepiolite, due to their great stability in sus-

pension, are also used as suspending agents in paints,

fertilizers, pharmaceuticals, and cosmetics. They are

also used for industrial cleaning of factory floors and

service station bays because of their capacity to

absorb grease and oil. These clay minerals also find

a widespread use as pet litter.

Further Reading

Boormans P (2004) Ceramics Are More Than Clay Alone.

Cambridge: Cambridge International Science Publishers.

Bundy WM (1991) Kaolin in paper filling and coating.

Applied Clay Science 5: 397–420.

Burst JF (1991) The application of clay minerals in ceram-

ics. Applied Clay Science 5: 421–423.

Murray HH (1991) Overview – clay mineral application.

Applied Clay Science 5: 379–395.

Murray HH, Bundy WM, and Harvey CC (eds.) (1993)

Kaolin Genesis and Utilization. Aurora, CO: Clay

Minerals Society.

Vaccari A (1999) Clay and catalysis: a promising future.

Applied Clay Science 14: 161–198.

COCCOLITHS

See FOSSIL PLANTS: Calcareous Algae

COLONIAL SURVEYS

A J Reedman, Mapperley, UK

Introduction

The organization of the systematic surveying of the

geology of the vast territories that formerly com-

prised the British Empire, mainly through the estab-

lishment of country specific geological surveys (see

Geological Surveys), has been a long process and

one that is not yet entirely complete. This article

outlines some of the major features of that process

with special attention being given to the role of the

organisation known as the Directorate of Colonial

Geological Surveys. Though the latter organization

was only in existence for less than twenty years, in

the middle of the last century, its influence on geo-

logical surveying in many parts of the world is still felt

to this day.

Early Days

In view of the fact that the Geological Survey of Great

Britain was established in 1835, it may seem surprising

that a systematic approach by the British Government

to establishing and nurturing Geological Surveys in the

many territories that constituted the British Empire

took a further one hundred and twelve years to come

to fruition, with the founding of the Directorate of

Colonial Geological Surveys in1947. A considerable

number of Geological Surveys had been established in

various British overseas territories well before 1947 but

largely through the lobbying efforts of enthusiastic

individuals, and usually through the local colonial

administration, rather than as a result of any over-

arching policy of the centralized colonial power vested

in the British Crown. The first of these local initiatives

was taken just seven years after the Geological Survey

of Britain came into being. In 1840, the former prov-

inces of Upper and Lower Canada were joined by an

Act of Union into a single province and a country called

Canada came into being. In 1842, the legislature of the

new country decided to set up a geological survey and

William Logan was appointed as its first director.

Shortly afterwards, in 1853, a geological survey for

India was established for India, based in Calcutta.

The Imperial Institute

The foundations for official British involvement in

overseas geology, administered from London, the

centre of the Empire, were laid through the opening

of the Imperial Institute in 1893. This organization

was established as the National Memorial of the Jubi-

lee of Queen Victoria and was initially funded by

grants from the Commissioners of the Great Exhib-

ition held in London in 1851. It was reorganized on a

number occasions during its relatively short life before

its final demise in the 1950s, but during this time it

contributed a great deal to geological knowledge of

the vast territories that constituted the ‘Empire’.

The prime purpose for the existence of the Imperial

Institute was to promote trade in natural raw

materials in the colonies and dependencies. Amongst

these commodities, minerals (see Mining Geology:

Mineral Reserves) were seen to be of great import-

ance and a Mineral Resources Department, later to

become a Division, was an important component of

370 COLONIAL SURVEYS

the establishment. In its early years, it carried out a

number of pioneering reconnaissance surveys in

colonial territories, mainly involving just one or two

geologists, often traversing whole countries on foot,

without the aid of any but the most rudimentary of

topographic maps. As interest in the Empire’s re-

sources grew, the Division increasingly concentrated

on providing services, such as mineral identification,

assaying, and economic assessment, to those fledgl-

ing geological surveys that were beginning to be

established.

A report published in the Bulletin of The Imperial

Institute in 1943 summarised the work of the Mineral

Resources Department during the fifty years it had

so far been in existence and also reviewed the likely

requirements for the future. Noting that some half

a million pounds had already been earmarked to

extend scientific investigation into ‘Colonial prob-

lems’, excluding welfare and development projects,

the report drew attention to ‘‘the wisdom of allo-

cating a fair share of any available grants to the

purpose of expanding the work of Geological

Surveying in the Colonial Empire’’. It noted that by

1943, local (overseas) geological departments existed

for territories with a total area of one and a quarter

million square miles (excluding the Dominions) but

that the total number of trained staff responsible for

geologically surveying this vast area amounted to

only forty six.

The early work of the Institute, mainly carrying out

reconnaissance surveys, was seen as a necessary pre-

liminary to the formation of a Geological Survey and

in a number of colonies this was achieved. Such col-

onies included British Malaya (now Malaysia, 1903),

Ceylon (now Sri Lanka, a Mineral Survey under vari-

ous subsequent names was established in 1903), the

Gold Coast (now Ghana, 1913), Uganda (1918),

Nigeria (1919), Tanganyika (Tanzania, 1926), Sierra

Leone (1927), Kenya (1933), and British Guiana

(Guyana, 1933) all established Surveys, often at-

tached to Mines Departments and with very few

geological specialists.

Directorate of Colonial

Geological Surveys

Though it was widely acknowledged that the Mineral

Resources Division of the Imperial Institute had

achieved a great deal in advancing knowledge of the

mineral resources of the colonies since its inception,

by 1943 it was also recognized that there was still a

serious lack of geological knowledge of much of the

extensive terrain that constituted the colonies and

that a new organization was needed to help rectify

this situation. A joint meeting of the Geological

Society of London and the Institution of Mining and

Metallurgy, after considering how geological surveys

in the British colonies might be strengthened in the

post-war era, made a number of recommendations.

The Secretary of State for the Colonies accepted the

advice of a committee set up to advise him on the need

for an expansion of geological work and how this

might be achieved, and on the first of January 1947,

a central organization for overseas Geological Surveys

was inaugurated in London with the appointment of

Dr Frank Dixey as its Director and as the Geological

Adviser to the Secretary of State. At the age of 54,

Dr Dixey had considerable experience of geological

surveying in the colonies, having successfully carried

out a reconnaissance survey of Sierra Leone followed

by almost eighteen years in Nyasaland, first as

Government Geologist and then Director of the Geo-

logical Survey where he was required to spend much

of his time and geological knowledge on the practical

problems of establishing, and improving, rural water

supplies. In 1939, the latter experience led him to be

appointed to set up a Water Department in Northern

Rhodesia (Zambia) and in 1944 he moved to Nigeria

as Director of the Geological Survey.

The Directorate of Colonial Geological Surveys

was initially housed in offices in the ornate Victorian

building originally constructed for the Imperial Insti-

tute in South Kensington, London. Work commenced

in a modest way; Dixey being joined by a geologist

and then, in 1949, by a geophysicist. Two Deputy

Director’s were appointed and the task of establishing

a photogeology section was commenced. In 1949, the

Colonial Office took over responsibility for the

Mineral Resources Division of the Imperial Institute

which, as the Mineral Resources Division of the Dir-

ectorate of Colonial Geological Surveys, continued

its wide-ranging work on the mineral resources of

the Colonial territories and compiling statistics on

mineral production throughout the Empire.

It soon became apparent that an increasing work-

load demanded an increase in the establishment and

investment on more modern equipment, with the cost

being met from Colonial Development and Welfare

funds. As well as continuing to service the specialist

needs of the eleven Geological Surveys that had been

previously set up in various the colonies with the

assistance of the Imperial Institute, it became clear

that some thirteen other territories could benefit

from the establishment of their own Geological

Surveys, and that the greatest need of both new and

pre-existing Surveys would be for an increase in

their staff complement of geologists, geophysicists,

and geochemists together with buildings and equip-

ment. While the costs were to be covered, during

their first few years, from Colonial Development

COLONIAL SURVEYS 371

and Welfare Funds, most territories eventually

assumed responsibility for the cost of their own

Geological Surveys.

By 1957, ten years after its foundation, the organ-

ization had grown very considerably and was able to

offer a broad range of services to the colonies, includ-

ing the recruitment of staff to serve in their Geological

Surveys. Apart from Dr Dixey, the Director, the or-

ganization now comprised a Directorate including

Geophysical and Photogeology Sections (total staff

9), a Mineral Resources Division (36 staff) and a

Joint Services Division (total staff 14) which included

a library and serviced both the Colonial Products

Laboratory and Colonial Geological Surveys.

The Mineral Resources Division not only continued

to give advice to Colonial Administrations on all

aspects of mineral development but was also respon-

sible for a new publication, ‘Colonial Geology and

Mineral Resources’, a successor to the Mineral Re-

sources section of the former ‘Bulletin of the Imperial

Institute’, and also continued to publish the ‘Statistical

Summary of the Minerals Industry’. Perhaps most

significant of all, at least as far as geological mapping

of the Colonial territories was concerned, was the

establishment of the Photogeological Section, shortly

to be housed in the Headquarters of Colonial (Geo-

detic and Topographic) Surveys where it was able to

access the considerable stock of air photographs being

built up by the latter organization.

Before 1947, geologists working in the Geological

Surveys of the colonies usually had to make their

own topographic maps by conventional surveying

methods and frequently in the absence of a reliable

trigonometrical network. The advent of air photo-

graphs not only allowed the greatly increased produc-

tion of topographic maps of many remote areas at a

scale adequate for geological mapping but also made

photographs available for geological interpretation.

Dixey reviewed the first nine years of Colonial Geo-

logical Surveys, and was able to report that, together

with the increase in geological staff, it was the topo-

graphic mapping programme of Colonial (Geodetic

and Topographic) Surveys that was more and more

responsible for the increased rate of geological map-

ping in the colonial territories. In the East African

territories of Kenya and Uganda for example, only a

total area of about 25 000 sq miles had been geologic-

ally mapped at various scales prior to 1947, but by

1993 that figure had increased by almost 75 000

square miles, all mapped at scales of either 1:50 000

or 1:125 000.

With respect to its establishment of a Geophysics

Section and, more particularly, a Photogeological Sec-

tion, Colonial Geological Surveys was ahead of its

much older sister organization, the Geological Survey

of Great Britain, with its nearby headquarters in Ex-

hibition Road in South Kensington. More innovation

was to follow under Dr Dixey’s leadership. With

the help of grants obtained from the Department of

Scientific and Industrial Research and the Colonial

Welfare and Development Fund, a Geochemical Pro-

specting Research Centre was set up at the Imperial

College of Science and Technology in London and

this laid the foundations for many subsequent geo-

chemical prospecting programmes both in the then

Colonial territories and, later, throughout many

other parts of the world. In 1957, grants were also

made available to set up an Isotope Research Group

in the Department of Geology and Mineralogy of

Oxford University and this group, expanding in future

years, was devoted primarily to problems in overseas

geology.

The task of promoting and assisting the forma-

tion of Geological Surveys in the Colonial Territories

and Dependencies, started by the Imperial Institute,

gained momentum after the inauguration of Colonial

Geological Surveys. In the first nine years of its exist-

ence, Geological Surveys had been established in a

further nine countries, as shown below:

The increase in the number of overseas ‘colonial’

Geological Surveys saw a marked increase in the

number of geologists, geochemists, and geophysicists

amongst their staff. In the first ten years of the Direct-

orate, the total rose almost fourfold from 58 to 212,

and to 258 by 1961. The Directorate acted as ad-

visers to the Colonial Office on matters of staff recruit-

ment and also ran a variety of training courses for both

individual and groups of newly recruited or established

staff of the Surveys. Secondment of specialists to

posts in colonial administrations or overseas Surveys

was also arranged. The demand for, and supply of

qualified professionals in the geological field varied

from year to year but the bulk of the new recruits

were young men just completing either their first or

second degrees and it is estimated that each year, be-

tween 1947 and 1955, Colonial Geological Surveys

absorbed between one quarter and one half of the UK

universities output of suitably qualified geologists.

Bechuanaland Protectorate (now Botswana) 1948

British Territories in Borneo (now mainly part of

Malaysia)

1949

Jamaica 1949

Swaziland 1949

British Solomon Islands Protectorate 1950

Cyprus 1950

Northern Rhodesia (now Zambia) 1950

Fiji 1951

Cyprus 1952

New Hebrides 1959

372 COLONIAL SURVEYS

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