Silicate clay are the electro-microscopic clay minerals, which diameter less than 2 microns.

1. Silicate Clay
Made By Group No: 03

2. Course Code: AG-3103
Course Title: Soil Physics and Chemistry
Roll No:
ASH1514009M
ASH1514020M
ASH1514026M
ASH1514027M
ASH1514028M
ASH1514O37M
ASH1514046M
ASH1514047M
ASH1514054M
ASH1514058M
ASH1414070M

3. Contents:
 Definition of Silicate Clay
 Some Important Features of Silicate Clays
 Basic Structure of Silicate Clays
 Classification of Silicate Clays
 Characteristics of Kaolinite minerals
 Characteristics of Mica minerals
 Characteristics of Vermiculite minerals
 Characteristics of Smectite minerals
 Characteristics of Chlorite minerals
 Characteristics of Interstartified minerals
 References

4. Definition of Silicate Clay:
Silicate clay are the electro-
microscopic clay minerals, which
diameter less than 2 microns. It is
the textural classes of soil and
developed more in the horizontal
axis than the vertical axis of soil
profile.
It is the characteristics minerals of
the earths near surface
environments. They form in soils
and sediments.
E.g: kaolinite, Micas, Vermiculite,
Chlorite etc.

5. Some Important Features of Silicate Clays:
Chemical Composition:
The chemical analysis of clay indicates the presence of silica, alumina,
iron and combined water. These make up from 90-98 percent of the
colloidal clay. The soil colloidal matter contains plant nutrients like Ca,
Mg and K etc.
Shape:
Silicate clay minerals have been examined by electron microscope and
found that the particles are laminated made up of layers of plates or
flakes or even rods. Each clay particle is made up of a large number of
plates like structural units.

6. Some Important Features of Silicate Clays:
Surface Area:
The surface area of a clay particle is usually defined as the area of the
particle that is accessible to ions or molecules when the clay is in an
aqueous solution. All clay particles (finer fraction of soil) must expose
a large amount of external surface.
Surface areas of clay particles can be measured by using
cetylpyridinium bromide (dissolving in water) for fully dispersed clay
suspension.
Surface area for clays like vermiculites and some mixed layer clays
300-500 m2/g; micaceous clays 100-300 m2/g; kaolinitic clays 5-100
m2/g; and amorphous clays have surface areas between 100 and 500
m2/g.

7. Some Important Features of Silicate Clays:
Electronegative Charge:
Clay micelles (micro cells) carry negative charges
and so a number of oppositely charged ions
(cations) are attracted to each colloidal clay crystal.
The colloidal clay particles have inner ionic layer
(surfaces of highly negative charge) and the outer
ionic layer (highly positive charge layer).
Adsorbed Cations:
Clay micelles adsorb a number of cations-humid,
arid and semiarid regions colloids-cations are H+,
Al3+, Ca2+, Mg/+, Na+ and K+. Cations adsorbed on the
clay colloids very oftenly determines the physical
and chemical properties of the soil and thereby
influence the plant growth.

8. Basic Structure of Silicate Clays:
Two structural units are involved in most of the silicate clay minerals.
They are
Tetrahedral silica sheets (Silica tetrahedral units)
Octahedral alumina sheets (Alumina octahedral units)
The tetrahedral silica sheets are attached to the octahedral alumina
sheet in the structure.

9. Tetrahedral Silica Sheet:
The main structural unit of
silicates is a tetrahedral cluster
containing one silicon atom and
four oxygen atoms. Three oxygen
in the sheet and one in the
above. The size of [SiO4]4-
tetrahedral is relatively stable,
with Si-O bond length varying
from 0.161 to 0.164 nm, O-to-O
distance about 0.264 nm.

10. Octahedral Alumina Sheet:
The alumina consists of two
sheets of closely packed oxygen
atoms or hydroxyl groups which
are held together by alumina
atoms in such a way that one
alumina is surrounded by six
oxygen atoms or hydroxyl group.
The normal O-to-O distance is
2.60A° and the common OH-to-
OH distance is about 3A ° .The
thickness of the unit is 5.05A° in
the clay mineral structure.

11. Classification of Silicate Clays:
A. Amorphous, e.g: Allophane group
B. Crystalline
a) 2 layer type(1:1 type)
i. Equidimensional (kaolin group), e.g: Kaolinite, Nacrite, Dickite,
Anauxite
ii. Elongate (halloysite group), e.g: Endellite, Metahalloysite
b) 3 layer type(2:1 type)
i. Expending lattice type
 Equidimentional
Smectite groups: e.g: Montmorillonite, Bidellite, Sauconite
Vermiculite groups: e.g: Vermiculite
 Elongate, e.g: Nontronite, Saponite, Hectorite

12. Classification of Silicate Clays:
ii. Non-expending lattice type
 Muscovite
 Biotite
 Phlogopite
c) Mixed layer type
 Chlorite group
d) Chain structure type
 Attapulgite
 Sepiolite
 Polygorskite

13. Characteristics of Kaolinite minerals:
• Name of Origin: Named after the locality.
• Color: White, Brownish white, Grayish
white, Yellowish white, Grayish green.
• Locality: Kao-Ling, China, Germany,
India, Australia, Malaysia, Brazil etc.
• Found in moist, warm to hot, sub-humid
and humid soils, acidic.
• Chemical Formula: Al2Si2O5(OH)4
• Composition: Molecular Weight = 258.16
gm(Al=20.90 %, Si=21.76 %, H=1.56 %,
O=55.78 %)

14. Characteristics of Kaolinite minerals:
• Surface area is kaolinite ranged
from 5-20 m2/g.
• It is one of the most wide spread
clay minerals in soils. It is most
abundant in soils of warm moist
climates and is a prominent
constituent of oceanic sediments.
• CEC usually vary from 3-15
meq(milliequivalent)/100g.

15. Characteristics of Mica minerals:
• Mica is a mineral name given to a group of
minerals. Of the 37 known species of the
mica group(Muscovite, Paragonite,
lepidolite, biotite etc.)
• They are all silicate minerals, known as
sheet silicates because they form in 2 silica
sheets with a central alumina sheet.
• Chemical Formula: The general formula
for minerals of the mica group is XY2–3
Z4O10(OH, F)2 with X = K, Na, Ba, Ca, Cs,
(H3O), (NH4); Y = Al, Mg, Fe2+, Li, Cr, Mn, V,
Zn; and Z = Si, Al, Fe3+,Be, Ti.
• Example: Lepidolite K(Li,Al)3(AlSi3O10)
(O,OH, F)2;Biotite K(Mg, Fe)3(AlSi3O10)
(OH)2; Muscovite KAl2(AlSi3O10)(OH)2

16. Characteristics of Mica minerals:
• Color: Purple, rosy, silver, dark green, brown,
black; yellowish-brown, green white; colorless.
• Specific gravity: 2.8-3.1 and Melting point: 700-
1000°C
• Jharkhand state in India had the largest
deposits of mica in the world, China, US, South
Korea Canada, Europe etc are found.
• Micas are fairly light and relatively soft. The
sheets are flexible. It is heat-resistant and does
not conduct electricity.
• CEC ranges from 15-40 meq/100kg.
• External surface area 70-100 m2/g and internal
area 1.0 nm

17. Characteristics of Vermiculite minerals:
• Vermiculite is a hydrated magnesium
aluminum silicate mineral.
• Found in Australia, Brazil, Bulgaria,
Kenya, Russia, South Africa, Uganda,
USA and Zimbabwe.
• Chemical Formula: (Mg, Fe++,Al)3
(Al,Si)4O10(OH)2•4(H2O)
• Composition: Molecular Weight =
504.19 gm(Mg=8.68 %, Al=23.01 %,
Fe=9.97 %, Si=5.57 %,H=2.00 %,
O=50.77%)
• Specific gravity: 2.4-2.7

18. Characteristics of Vermiculite minerals:
• Color: Colorless, Green, Gray white,
Yellow brown.
• CEC ranges from 100-180
meq/100kg.
• External surface area 500-600
m2/g and internal area 1-1.5 m2/g.
• Shape of the vermiculites are
platy, flakes.

19. Characteristics of Smectite minerals:
• Members of the smectite minerals can be
divided into 2 groups. The dioctahedral
minerals (montmorillonite, beidellite,
and Nontronite) and the trioctahedral
minerals (hectorite, saponite, and
sauconite.
• Size: Naturally occurring smectite ranges
in size from 0.25 microns up to 0.75
microns.
• Shape: Irregular flakes.

20. Characteristics of Smectite minerals:
• They are characterized by alumina
octahedral layer sandwiched
between two silica tetrahedral
layers.
• CEC ranges varies from 80-150
meq/100g soil.
• Specific surface area ranges from
700-800 m2/g

21. Characteristics of Chlorite minerals:
• Chlorites are basically iron-manganese
silicates with some aluminum present.
• Members of the chlorites minerals are
Clinochlore, Nimite, Ripidolite, Odinite
etc.
• Chemical Formula:
(Mg,Fe)3(Si,Al)4O10(OH)2·(Mg,Fe)3(OH)6
• Color: Various shades of green; rarely
yellow, red, or white.

22. Characteristics of Chlorite minerals:
• Chlorite is commonly found
in igneous rocks, sedimentary
rocks and metamorphic.
• Specific gravity: 2.6-3.3
• Chlorite is so soft that it can be
scratched by a finger nail.

23. Characteristics of Interstartified minerals:
• Many clay materials are mixtures
of more than one clay mineral.
Such minerals are called as mixed
layer or interstratified minerals.
E.g: Chlorite-vermiculite, Mica-
Smectite.
• As the mixing ratio for the two
component layers varies.
References:
 https://en.wikipedia.org/wiki
 White R.E., 1987. Introduction to the
Principles and Practice of Soil Science.

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