GLG212

Clay MineralsGroup MineralG.D.J. Scholtz, 2010130470

4/17/2013

Figure 1: A picture of clay chips. (http://www.pitt.edu/~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Muscovite_Clays/ShaleChipsRedHultonBridge.jpg)

Abstractin this report the clay group minerals will be discussed and

explained. there are a lot of clay minerals on the earth, and to

simplify this report the minerals are arranged according to their

groups. there are four main group minerals, and three minor ones

that are considered clay minerals. the main mineral groups are the

kaolinite group, the illite group, the montmorillonite group and the

chlorite group. the minor groups are the halloysite group, the

attapulgite group, and the allophane group. the groups will then be

further subdivided into their respective minerals that are

associated with that group. the physical and optical properties will

be given for the clay minerals and they will be briefly explained.

all the names and the chemical formulas will be given for all the

minerals in this group as well as a quick description on how to

distinguish between these minerals. in this report you will also

find a short description of the crystal chemical structure of the

group of minerals. the way in which this influences the optical and

physical properties of the minerals will also be mentioned. Finally

the economical importance of this group will be discussed.

Table of ContentsAbstract...........................................................2Introduction.......................................................2

Physical Properties of Clay Minerals...............................3Optical Properties of Clay Minerals................................4

Describe the general crystal chemical structure* of this group of minerals and an explain of how this influences the optical and physical properties of these minerals..............................5

G.D.J. Scholtz 2010130470 2

Names and Chemical Formulas Of Minerals Found in The Clay Mineral Group as well as How They can be Distinguished from Each Other.....6

Economic Importance of Clay Minerals...............................7Conclusion.........................................................8

References.........................................................8

G.D.J. Scholtz 2010130470 3

Table of FigureFigure 1: A picture of clay chips. (http://www.pitt.edu/~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Muscovite_Clays/ShaleChipsRedHultonBridge.jpg)..................1Figure 2: A electo magnetic microscope picture of a clay mineral. (http://www.claysandminerals.com/materials/shales).................4Figure 3: A illustration of The Chrystal chemical structure of Montmorillonite. (http://serc.carleton.edu/NAGTWorkshops/mineralogy/clay_mineralogy.html)...............................................................7Figure 4: above is a picture of the Kaolinite in china. (http://www.claysandminerals.com/materials/shales).................8

List of tablesTable 1:This is a table of the main clay minerals and their physicalproperties (Velde 1992, pg110).....................................4Table 2: This is a table of all the main clay minerals and their optical properties (Bosazza 1942, pg76-77).........................5

IntroductionThe clay minerals are not the most important mineral groups of all

the groups put they are important none the less. Clay minerals are

studied in many fields, but the fields that handle these minerals

the most are mineralogy and soil science. this group is part of the

phyllosilicates, which are plate silicates. the clay minerals are so

important because they form the soils that are needed for

agriculture and most surfaces on the planet is covered with soils,

therefore they are covered with clay minerals. the reason behind the

importance of clay minerals are that they contain water in

alternating amounts or percentages between the sheets of silica, and

they also have the ability to transfer of substitution of their

G.D.J. Scholtz 2010130470 4

cations. this is also the difference between the rest of the

phyllosilicates and the clay minerals (Velde 1992, pg36). Clay

Minerals are mostly found in the very vine or clay sized fraction of

the soils, sediments, sedimentary rock, and weathered material. the

clay minerals are usually grouped according to their structure. this

is according to TO or TOT as well as the difference between

trioctahedral or dioctahedral. the T is the tetrahedral silica layer

and the O is the octahedral layer. In the optical slide it is very

difficult to identify the different clay minerals from one another

so it is recommended to use different techniques to establish the

different minerals ( Williams 2009, pg178) .

most clay minerals are the product of weathering of other rock and

mineral products. there are only one or two clay minerals that can

be found in igneous rocks. Clay minerals can be found in soils,

sedimentary rocks, sediment, and altered rock (Bosazza 1942, pg 32).

G.D.J. Scholtz 2010130470 5

Figure 2: A electromagnetic microscope picture of a clay mineral. (http://www.claysandminerals.com/materials/shales)

Physical Properties of Clay MineralsTable 1:This is a table of the main clay minerals and their physical properties (Velde 1992, pg110)

Group Name Mineral Name

Chemical formula

Streak

Luster

Hardness

Crystal System

Color Cleavage

Kaolinite Kaolinite and Anauxite

Al2Si2O5(OH)4 White

Earthy

1.5-2 Triclinic

White,Brown,Yellow

{001} Perfect

Nacrite Al2Si2O5(OH)4 White

Pearly

1 Monoclinic

Colorless, White,Brown,Yellow

{001} Perfect

Dickite Al2Si2O5(OH)4 White

Pearly

1.5-2 Monoclinic

Blue, Colorless,

{001} Perfect

G.D.J. Scholtz 2010130470 6

Gray, Yellow,White

Montmorillonite

Montmorillonite

(Na,Ca)0,3(al,Mg)2Si4O10(OH)2.n(H2O)

White

Earthy

1.5-2 Monoclinic

Colorless, White,Brown,Yellow

{001} Perfect

Beidellite Na0.5Al2.5Si3.5O10(OH)2.(H2O)

White

Earthy

1-2 Monoclinic

White,Brown,Yellow, Red,Gray

{001} Perfect

Nontronite Na 0.3 Fe3+

2Si3AlO10(OH)2.4(H2O)

White

Earthy

1.5-2 Monoclinic

Green,Brown,Yellow

{001} Perfect

Saponite Ca0.1Na0.1Mg2.25

Fe2+0.75Si3AlO10

(OH)2.4(H2O)

White

Earthy

1.5-2 Monoclinic

Blue, Colorless, Gray, Yellow, White

{001} Perfect

Illite K0.6(H3O)0.4Al1.

3Mg0.3Fe2+0.1Si3.

5O10(OH)2.(H2O)

White

Earthy

2.6-2.9

Monoclinic

White {001} Perfect

Halloysite Halloysite Al2Si2O5(OH)4 White

Earthy

2 Monoclinic

White,Brown,Yellow, Red,Gray

{001} Perfect

Hydrated halloysite

Al2Si2O5(OH)4 White

Earthy

2 Monoclinic

White,Brown,Yellow, Red,Gray

{001} Perfect

Allophane (Al2O3)(SiO2)1.3.2.5(H2O)

White

Waxy 3 Amorphous

Green,Brown,Yellow, White,Blue

none

G.D.J. Scholtz 2010130470 7

Optical Properties of Clay MineralsTable 2: This is a table of all the main clay minerals and their optical properties(Bosazza 1942, pg76-77)

Group Name Mineral Name y B A Y-a 2v(in degrees)

Optical character

Extinction(in degrees)

Kaolinite Kaolinite and Anauxite

1.570-1.500

1.569-1.559

1.563-1.553

0.006

24-50

(-)

1-3.5

Nacrite 1.566-1.563

1.563-1.562

1.560-1.557

0.006

40-90

(-) or(+)

10-12

Dickite 1.566

1.563-1.561

1.560

0.006

52-80

(+)

15-20

Montmorillonite

Montmorillonite 1.530-1.500

1.505-1.470

0.035-0.025

7-25

(-)

Beidellite 1.500-1.530

1.530-1500

0.035-0.025

Small

(-)

Nontronite 1.610-1.560

1.575-1.530

0.035-0.030

small

(-)

Saponite Indices of refraction similar to Montmorillonite

Illite 1.605-1.56

1.570-1.53

0.035-0.03

Small

(-)

G.D.J. Scholtz 2010130470 8

5 5 0Halloysite Halloysite Mean index =

1.561-1.549Veryslight

Hydrated halloysite

Mean index = 1.542-1.526

Veryslight

Allophane Amorphous n = 1.496-1.470

Mg- Clay minerals Some of these indices of refraction similar to those of Montmorillonite

Describe the general crystal chemical structure* of this group

of minerals and an explain of how this influences the optical

and physical properties of these minerals. They are normally made of layers of tetrahedral and octahedral

layers that alternate in a certain way. there are in some minerals

in this group that have H2O atoms and some other atoms between the

layers of TO and TOT. this is the reason for clay minerals to be

able to have such a high cation exchange, and this is the reason why

clay minerals can take up so much water. this is also the reason for

the exaggerated expansion and retraction of the clay minerals. the

cations that can go in the openings between the layers is the reason

for the variety of colors that these minerals come in. for example,

high water content in the mineral will make it slightly blue. Pure

Kaolinite is actual white but the impurities is what give this

mineral its different colors.

This cation exchange in the clay minerals is very important to the

soils. it is referred to, by soil scientists as the cation exchange

rate. (Wenk and Bulakh 2004, pg464)

G.D.J. Scholtz 2010130470 9

Figure 3: A illustration of The Chrystal chemical structure of Montmorillonite.(http://serc.carleton.edu/NAGTWorkshops/mineralogy/clay_mineralogy.html)

Names and Chemical Formulas Of Minerals Found in The Clay

Mineral Group as well as How They can be Distinguished from

Each Otherthe main mineral groups are the Kaolinite group, the Illite group,

the Montmorillonite group and the chlorite group. the minor groups

are the halloysite group, the attapulgite group, and the allophane

group. (Bosazza 1942, pg 32).

G.D.J. Scholtz 2010130470 10

Kaolinite group: this group has the chemical formula of

Al2Si2O5(OH)4, and can be differentiated from the other groups by

looking at the luster in general.

Illite group: This group has a chemical formula of (K,H3O)

(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)], and can be differentiated by

the fact that it is generally harder than the rest of the

groups.

Montmorillonite group: This group has a chemical formula of

(Na,Ca)0,3(al,Mg)2Si4O10(OH)2.n(H2O) and can be differentiated by

the fact that it is almost always in granular form.

Chlorite group: This group has a chemical formula of

(Mg,Fe)3(Si,Al)4O10(OH)2(Mg,Fe)3(OH)6. easily distinguished by

its pearly luster.

Economic Importance of Clay Minerals

Clays are very economically important as they are used is a variety

of industries. clay is probably the most important constituent of

soils as this is where the cater content of the soils are stored, as

well as the cation exchange that is present in clay minerals. both

of these factors make it important for the agricultural industry.

Kaolinite is also used for the manufacture of porcelain in china.

(Miers 1902, pg447)

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Figure 4: above is a picture of the Kaolinite in china.(http://www.claysandminerals.com/materials/shales)

Conclusionthere are a lot of clay minerals on earth and they have a very

important job, there will be no live on earth without them. the

identification of clay minerals is also very important as they are

very similar and the structure is very complex.

G.D.J. Scholtz 2010130470 12

ReferencesB. Velde (1992). Introduction to Clay Minerals, Chemistry, origins,

uses, and environmental significance. Chapman and Hall, . (198pg)

Hans-Rudolf Wenk and Andrei Bulakh (2004). Minerals Their Constitution and

Origin, . New York: Cambridge University Press, 646pg.

Henry A. Miers (1902). Mineralogy an Introduction to the Scientific study of

Minerals, . New York: The Machillan Company, 584.

V.l. Bosazza (1942). The petrography and Petrology of South African

Clays. Natal University College, Johannesburg. (313pg).

William D. Nesse (2009). Introduction to Optical Mineralogy, International

edition. New York: Oxford University Press, 348pg.

(Date created/last updated). Title of Document, Available from: www.example.eg.eg (Date Accessed).

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