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•Silicates occur in the earth’s crust in the
form of silicates minerals and aluminosilicate
•The silicates are the largest, the most
interesting and the most complicated class of
minerals than any other minerals.
• Approximately 30% of all minerals are
silicates and some geologists estimate that
90% of the Earth's crust is made up of
silicates, SiO4- based material.
•oxygen and silicon are the two most abundant
elements in the earth's crust.
- 95% of All
- Silicon (Si) and
Oxygen (O) bond
Silicon and Oxygen
SINGLE SILICA TETRAHEDRON
• Sodium silicates is the only common silicate which
is soluble in water
• Most of the silicates are insoluble in water .this
is due to great strength of Si-O bond this bond
can be broken only on treatment with strong
reagents like hydrofluoric acid.
• The Si-O bond – 50% covalent, 50% ionic
• Electronegativity of O is 3.5 and of Si is 1.9
difference is 1.6.
4- tetrahedra which
• All silicates comprises of SiO4
are formed by sp3 hybrisidisation of Si orbitals.Si
forms 4 bonds with oxygen atoms.
All silicates contains the tetrahedral SiO4
Sodium silicate is commonly manufactured
using a reaction in liquid phase or in solid
phase. Both processes use alkaline and quartz
sand as raw materials
A mixture of caustic soda, quartz sand, and
water are prepared in a mixing tank, then fed
into a reactor, where steam is introduced. The
n SiO2 + 2 NaOH → Na2O•nSiO2 + H2O
• This process uses quartz sand with either
sodium carbonate or sodium sulfate. The feed
materials are heated in a reflection furnace.
The reaction is
Na2CO3 + x SiO2 → (Na2O)•(SiO2)x + CO2
2 Na2SO4 + C + 2 SiO2 → 2 Na2SiO3 + 2 SO2 +
Talc is primarily formed via hydration and
carbonation via the following reaction;
serpentine + carbon dioxide→ talc+ magnesite+ water
2 Mg3Si2O5(OH)4 + 3CO2 → Mg3Si4O10(OH)2 + 3
MgCO3 + 3 H2O
Talc can also be formed via a reaction between
dolomite and silica,
dolomite+ silica+ water → talc + calcite+ carbon dioxide
3 CaMg(CO3)2 + 4 SiO2 + H2O → Mg3Si4O10(OH)2 + 3
CaCO3 + 3 CO2
ZSM-5 is a synthetic zeolite. There are many ways
to synthesize ZSM-5, a common method is as
SiO2 + NaAlO2 + NaOH + N(CH2CH2CH3)4Br + H2O →
ZSM-5 + analcime + alpha-quartz
ZSM-5 is typically prepared at high temperature
and high pressure in a Teflon-coated
autoclave and can be prepared using
varying ratios of SiO2 and Al containing
Different types of silicates
Ring and chain silicates
Double chain silicates
Silicates with sheet structures
Silicates with 3-dimensional framework
• Orthosilicates are minerals consisting of only
4- units. The cations are some other
• the following minerals are orthosilicates:The Be
and Zn ions are tetrahedrally bonded to the
oxygen of the silicate in these two minerals:
phenacite, Be2SiO4 and willemite, Zn2SiO4 ,zircon.
• In olivine, (Fe, Mg)2SiO4, the cations are
either Fe2+ or Mg2+.
• This formula suggests that this mineral is a
mixed salt of iron and magnesium silicates.
• These cations are octahedrally coordinated to
the oxygen atoms of the silicate.
• Pure salt Fe2SiO4 is called fayalite, and
Mg2SiO4 is called forsterite.
4- units are linked together, they
• When two SiO4
6-. For example,
form the pyrosilicate group, Si2O7
thortveitite, Sc2Si2O7 is a pyrosilicate,
hemimorphite [Zn4(OH)2Si2O7 ]
Ring and chain silicates
4- units share with other SiO4
• When two oxygen of SiO4
units, the silicates form a ring or an infinite chain.
• The stoichiometry of the silicates becomes (SiO3)n
Benitoite BaTi(SiO3)3 contain three silica rings.
• The precious stone beryl Be3Al2(SiO3)6 contain six-silica
• Single chain silica are called pyroxenes.
• Some synthetic silicates Na2(SiO3) have been
shown to contain the simple chain silicates
• in which the Si-O bonds of the type Si-O-Si
are 168 nm, with the Si-O-Si angles of 137o.
The Si=O bonds are shorter, 1.57 nm.
• The natural pyroxenes include enstatite,
MgSiO3, diopside, CaMg(SiO3)2, and jadeite,
NaAl(SiO3)2, Spodumene LiAl(SiO3)2
Double chain silicates
• Double chain silicates are called amphiboles, chains have a
stoichiometry of (Si4O11)n
• Tremolite, Ca2Mg5(Si4O11)2(OH)2, is such a mineral.
• crocidolite Na2Fe3
IIISi8O22(OH)2 or blue asbestos
consist of double chain silicates.
• Asbestoses have been identified as carcinogens, and its
application has since been limited due to a ban to limit its
exposure to the public.
• Most comercial asbestoses are chrysotile, which contain
layers of silicate sheet
Structure of Double chain silicates basic unit is
Silicates with sheet structures
• Sheet slilicates are called phyllosilicates (phyllo
• These silicates are easy to cleave (as does
• Talc is a typical sheet silicate, Mg3(OH)2(Si2O5 ).
Talc is a main ingredient of the soapstone
• Formed by sharing 3 bridging O per Si atom.
• Sometimes Si atoms are partly replaced by Al
atoms. Eg-Biotite K(MgFe)3(OH)3(AlSi3O10),
Silicates with 3-dimensional
• the SiO4
4- units can share every oxygen with other
units to form a three dimensional network, and
quartz has such a structure.
• In this arrangement, the stoichiometry is reduced
to SiO2, which is often called silica. A collection of
small pieces of quartz is sand.
• when some of the Si4+ ions in silicates are replaced
by Al3+ ions.
• For each Si4+ ion replaced by an Al3+, the charge
must be balanced by having other positive ions such
as Na+, K+, and Ca2+ ions.
• Radius ratio is .43 close to CN 4 to 6
• Sanidine, [(K,Na)AlSi3O8]4
Orthoclase, [(K, Na)AlSi3O8]4
• The alkali ions are held in place to balance the
charges due to the presence of Al3+ ions
instead of Si4+ ions.
• The Al3+ ions replace Si4+ ions in the chains of
corner shared tetrahedra of SiO4 groups.
• However, the bonding between Al and Si can
• Silicon atoms or ion tend to be bonded to 4
oxygen atoms in a tetrahedral fashion, but
aluminum ions tend to be bonded to 6 oxygen
atoms in an octahedral fashion.
Micas are amphiboles made up of sheets of
4- is replaced by (AlO4)5-
tetrahedre in which SiO4
They are chemically inert and thermally stable
have high dielectric constant.
Due to which micas are used in furnance windows
and electrical appliances.
powdered mica is used as a filters for rubbers
plastics and insulation boards
• Produced by weatering and decomposition of
• Eg- china clay Al2(OH)4Si2O5,.e kaoline has sheet
structure sheets are hald by OH bridges.
• Used in making chinaware, fire bricks etc
• At 900°C clay forms multite Al6SiO2O13. this has
• It is montmorillonite in which principle
exchangable ion is Ca+2.
• Ii has strong absorbtive power and cation
• Used as adsorbent and cation exchanger.
• is a class of hydrated aluminosilicates found
in certain volcanic rocks.
• Once upon a time, geologists thought these
minerals were interesting because they
consist of large cage-like structures with
• Today, these materials are highly valued for
• Zeolites have a porous structure that can
accommodate a wide variety of cations, such as
Na+, K+, Ca2+, Mg2+ and others. These positive
ions are rather loosely held and can readily be
exchanged for others in a contact solution.
• An example mineral formula is:
Na2Al2Si3O10·2H2O, the formula for natrolite.
• The name 'zeolite' is said to have its origin in
the two Greek words zeo and lithos which mean
'to boil' and 'a stone'.
• The phenomena of melting and boiling at the
same time is a novel property.
• The name 'zeolite' was first used by
the Swedish mineralogist Axel Fredrik
Cronsted , the first recognized mineral zeolite,
which was discovered in 1756.
• Zeolites are the aluminosilicate members of
the family of microporous solids known as
• The term molecular sieve refers to a
particular property of these materials, i.e., the
ability to selectively sort molecules based
primarily on a size exclusion process.
• At present over 150 synthetic zeolites &
zeotypes and 40 natural zeolites are
known. Synthesis of zeolite is a very active
field of study
• industrially important zeolites are produced
• Typical procedures heating aqueous solutions
of alumina and silica with sodium hydroxide.
• Equivalent reagents include sodium aluminate
and sodium silicate.
• Further variations include changes in the cations to
include quaternary ammonium cations.
• there are many different kinds of zeolites, each
with a definite structure and associate with it are
• In terms of applications, we are assuming zeolites
as porous aluminosilicates with large tunnels and
cages for a fluid (gas and liquid) to pass through.
• The applications are based on the interactions
between the fluid phase and the atoms or ions of
IN GENERAL TERMS, ZEOLITES HAVE MANY
• As selective and strong adsorbers: remove
toxic material, selective concentrate a
particular chemical, as Molecular Sieve.
• As selective ion exchangers: for example used
in water softener.
• Superb solid acid catalysts, when the cations
are protons H+.
• As catalysts, their environmental advantages include
decreased corrosion, improved handling, decreased
environmentally toxic waste and minimal undesirable
• As builder a material that enhance or protecting the
cleaning power of a detergent.
• Sodium aluminosilicate is an ion exchange builder often used
in lundary detergent as a builder.
• A builder inactive the hardness of water by either keeping
calcium ions in solution, by precipitation, or by ion exchange.
APPLICATIONS OF SILICATES
• Unique properties of silicates include the ability to
conduct electricity, produce a high-frequency vibration
and provide thermal insulation.
• Silicon is the central component of silicates.
• It is a very hard crystal that can be cut to minuscule
sizes, and it conducts electricity.
• It is because of these characteristics that silicon is
the perfect material to make microchips, which run
every computer, cell phone and gaming device.
• Quartz crystals are another silicate with a
unique ability to produce a rhythmic high-frequency
• For this reason, these crystals are used to
make oscillators used in watches, radios and
• Silicates are also used to make glass and ceramics.
• To do so, hard, formless material like sand or
ceramic clay is heated to high temperatures,
turning it into malleable material that can be
formed to make drinking glasses,
• Silicate ceramics have clearly defined thermal
properties and, as such, are particularly useful
for advanced engineering and technology.
• For example, silicate ceramic tiles are used on
the space shuttle to shield it from the extreme
temperatures of the outer atmosphere.
High and Low Technology
• Silicates are the most abundant mineral class on
• In general, they are hard and cut easily to micro
pieces, produce a rhythmic high-frequency
vibration, and provide thermal insulation
• These unique characteristics make them highly
useful for myriad high- and low-tech products,
from microchips to watches