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What is Talc?
• Chemistry: Mg3Si4O10(OH)2, Magnesium Silicate Hydroxide
• Class: Silicates
• Subclass: phyllosilicates
• Group: Clays and also The Montmorillonite/ Smectite Group.
• Uses: an ornamental and heat, acid and electrically-resistant stone (soapstone)
used as counter tops, electrical
switchboards, carvings, etc, used as an
ingredient in paints, rubber, roofing
materials, ceramics and insecticides.
Most commonly known as the primary
ingredient in talcum powder.
Talc is an important industrial mineral.
Its resistance to heat, electricity and
acids make it an ideal surface for lab
counter tops and electrical switchboards. It is also an important
filler material for paints, rubber and
insecticides. Even with all these uses,
most people only know talc as the
primary ingredient in talcum powder.
Mineral specimens are not very common as
it does not form very large crystals.
However, it often replaces other
minerals on an atom by atom basis and
forms what are called pseudo morphs
(false shape). The talc takes the form
of the mineral it replaces. A specimen
of what looks like milky quartz is quite
a surprise when it not only has a soapy
feel but can be scratched by a fingernail.Talc General Information
| Empirical Formula: |
Mg3Si4O10(OH)2 |
| Environment: |
Hydrothermal alteration of
non-aluminous magnesian
silicates. |
| IMA Status: |
Valid Species (Pre-IMA) 1546 |
| Name Origin: |
From the Arabic. |
| Synonym: |
Kerolite, Magnesium Talc,
Soapstone, Steatite - massive |
There are important deposits of talc
in Austria, Italy, France, and Canada
and in the United States in California,
North Carolina, Texas, Georgia, and
Montana. Talc is used in making paper
(as a filler), paints, face and talcum
powder, soap, fireproof roofing, foundry
facings, lubricants, linoleum and
oilcloth, electrical insulation, and pottery.
TALC is also written as H2Mg3(SiO3)4,
which corresponds to 4.8% H2O;
31.7% MgO and 63.5% SiO2. It is essentially a secondary mineral
formed by the hydrothermal actions and
regional metamorphism of magnesium rich
rocks like dolomite, pyroxenite,
amphibolite, seerpentine, dunite and chlorite.
In pulverized form it is whiter in
appearance. The compact variety of talc
is called steatite or soapstone. The
word soapstone has been named probably
due to its soapy feel. The impure and
hard variety is called potstone, which
is mainly utilized for making carvings,
models, decorative vases, utensils, pots
and the like and hence the name
potstone.
French-chalk is the trade name of
pulverized talc of pure white quality
which forms the base for many cosmetics
and toilet preparations. Talc is valued
for its extreme softness, smoothness,
high lubricating and hiding power and
ability to absorb oil and grease. It is
chemically inert to acids and alkalies.
It has been found to be an excellent
filler. It can withstand temperatures
upto 1300ºC. It has law electrical and
thermal conductivity. Above all it can
be easily powdered, cut and sawn into
any shape and size. These properties in
talc are of extreme value for various
industrial applications described later
in this chapter.
Talc is found in three forms, fibrous,
nonfibrous and massive. The fibrous
variety consists of rich proportions of
tremolite, anthophyllite, and
serpentine. The nonfibrous variety
contains mostly of srpentine and
carbonates. Fibrous variety is slightly difficult to grind.
Talc Physical Properties
| Hardness |
1 (can leave mark on paper) |
| Specific gravity |
2.7 - 2.8 (average) g/cm3 |
| Cleavage |
Perfect in one direction,
basal |
| Color |
Pale green, White, Gray white, Yellowish white, Brownish white. |
| Fracture |
Uneven to lamellar |
| Crystal habits |
never in large individual
crystals, but if found are
flattened tabular crystals with
a hexagonal cross-section,
usually talc is found in compact
or lamellar masses. Forms pseudo
morphs (false shape) of other
crystals such as quartz, pyroxenes, olivine and amphiboles. |
| Luster |
Vitreous, Pearly, Waxy |
| Streak |
White |
| Transparency crystals |
Translucent and masses are
opaque. |
| Crystal system |
Trigonal; bar 3 2/m |
| Other Characteristics |
Cleavage flakes are slightly
flexible but not elastic and
talc has a soapy feel to the
touch |
| Associated |
Minerals include serpentine, dolomite, magnesite, quartz, pyroxenes, olivine, biotite and amphiboles. |
| Best Field |
Indicators softness, color,
soapy feel, luster and cleavage. |
Talc Crystallography
| Axial Ratios |
a:b:c =0.5778:1:2.0668 |
| Cell Dimensions |
a = 5.27, b =
9.12, c = 18.85, Z = 4; beta =
100.016° V = 892.17 Den(Calc)=
2.82 |
| Crystal System |
Monoclinic - Prismatic-M Symbol (2/m) Space Group: C 2/c |
| X Ray Diffraction |
By Intensity (I/Io): 9.35(1), 1.53(0.55), 4.59(0.45) |
Other specification according to API or OCMA standards.
Optical Properties
| Gladstone-Dale |
CI meas= 0.018 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= 0.042 (Good)- where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2028,KPDmeas= 0.208, KC= 0.2117 |
| Optical Data |
Biaxial (-), a=1.538-1.55, b=1.575-1.594, g=1.575-1.6, bire=0.0370-0.0500,
2V(Calc)=0-38, 2V(Meas)=0-30. Dispersion noticeable, r > v |
| Pleochroism (x) |
Colorless |
| Pleochroism (y) |
Pale green |
| Pleochroism (z) |
Pale green |
Talc Calculated Properties
| Electron Density |
ſelectron=2.76 gm/cc
note: ſTalc=2.75 gm/cc.
|
| Photoelectric |
PETalc = 1.57 barns/electron
U=PETalcX ſelectron= 4.34 barns/cc |
| Radioactivity |
GRapi = 0 (Gamma Ray American Petroleum Institute Units) |
Talc is Not Radioactive
Talc Industrial Applications
Talc is one of the most important
industrial minerals and is the most
common mineral for daily use as a body
and face powder. Talcum Powder, the name
derived from the mineral itself, is used
in most urban homes the world over. The
invention of perfumed talcum powder has
been a contributing factor in the growth
of modern fashions in cosmetics. The use
of talc was known to civilisations in
antiquity. The ancient craftsmen of the
Mohenjodaro and Harappa civilisation,
(in Sind, now in Pakistan), about 5000
years ago, exercised their skill on
steatite, engraving their seals with
representations of animals and
mythological signs, before subjecting
the carving to heat to acquire hard,
white lustrous, enamelled surfaces.
Small sculptures, ornate bosses and
vessels were also made from the mineral
during those early times.
Pulverized talc has wide industrial
applications as filler in rubber,
textile, plastic, linoleum, asbestos
products, polishes and soaps; as a
loading agent for paper of all kinds; as
a carrier of insecticidal and pesticidal
dusts and for coating calcium ammonium
fertiliser. Most of the rubber
manufacturers use talc powder as a
lubricant to prevent ungalvanized rubber
goods from sticking. The purer variety
of steatite after calcination,
industrially called 'Lava' is used in
the manufacture of law loss ceramic
materials required for high frequency
insulations in all kinds of radio,
television and related instruments.
Bricks made out of crushed steatite
bonded by sodium silicate are used for
ssthe manufacture of furnaces in which
argentiferous lead is softened before
desilverising. Paper industry accounts
for about 50% of the total consumption,
in the domestic industry, 15% is shared
by the insecticide and pesticide
industries and only 3% by talcum powder
manufacturers. The remaining quantity is
consumed in textile, ceramics, paints,
rubber, foundry facing and other industries.
Paper
Talc both in pulverized and brick forms,
are used in this industry. Pulverized
material of 200-300 BSS sieve is
required as filler. It is used in the
same way as china clay, that is, the
talc powder is mixed with pulp before
making into paper. A number of paper
manufacturers are changing over from the
use of china clay to French chalk as
filler and loading material. The
brightness in talc is 85 to 88º as
compared to 75º in china clay. Since
1960, the consumption of talc in the
paper industry has greatly increased.
Paper industry requires talc powder,
known as French chalk, of pure white
quality. It should be free from gritty
material. It should have law CaCO3
content, not exceeding 4%; also FeO
should not be more stha 2%. Off-colour
variety of talc free from grit is used
for brown, roofing or inferior type of
paper. Soapstone bricks are used for
lining pulp tanks in the paper industry.
Textiles
Textile industry also prefers talc
powder free from grit and colouration,
which is used both for loading and
bleaching certain types of cotton goods.
Inferior grades are used in back filling textiles.
Cosmetics
In the manufacture of body and face
powder, finely pulverized talc of very
high purity is required. The material is
generally reduced to fine particles by
micronising. Cosmetics are prepared with
a base of talc to which are added
covering agents like pigments and
adhesives, starches and perfumes. A
common adhesive is zinc stearate. It is
now being fast substituted by lithium
stearate. In the manufacture of
dentrifices some quantity of talc is
used, here as a polishing agent.
Dentrifices are prepared by mixing
suitable proportions of polishing agents
like talc, precipitated limestone,
kaolin, calcium sulphate, calcium
phosphate with gum, glycerin, soap and
other chemical ingredients.
The pharmaceutical industry requires
talc containing less than 0.1% FeO.
Natural material of such purity is
generally not found and pharmaceutical
talc is preferred by passing the high
purity powdered talc over a magnetic
separator to reduce the iron content.
Rubber
In rubber industry talc is used for two
purposes, one to prevent rubber moulds
from sticking and the other as
compunding material in the preparation
of certain types of hard rubber. The
consumption of talc for the latter use
is small. Generally grade II to III are
used in the rubber industry. Talc should
be of fine mesh all passing through 200 mesh.
Ceramics
Talc is increasingly being used in the
manufacture of artwares, jars, wall and
floor tiles. It serves as a non-plastic
ceramic material. The addition of talc
in suitable proportions in the body of
mixtures for porcelain, jars etc.
prevents the crazing (cracking) effect
on the glazes. The proportion of talc in
the ceramic body may go upto 80%. It is
valued for its refractoriness and
stability, as well as extremely law
shrinkage at high temperature. Talc
converts into clino-enstatite at about
1300º C. Between 800ºC to 840ºC, the
water molecules are driven off and talc
dissociates into enstatite and amorphous
silica without undergoing any change in
shape, the shrinkage being 0.0005 inch only.
In the manufacture of ceramic goods
required for the electrical industry,
the talc should not contain more than
1.5% FeO and CaO. Some consumers do not
regard CaO as having any harmful effect.
Steatite suitable for the manufacture of
'lava' insulators must he dense,
compact, uniform and homogeneous
intexture, free from any inclusion and
parting planes. It should not contain
CaO more than 1.5% and Fe2O3; more than
1%. The iron oxide is a colourant and
gives the fired shapes an unattractive
colour. An increase of iron oxide above
two per cent decreases the 'Q' value
(ratio of reactance to resistance) and
increases the dielectric constant. CaO
imparts abrasiveness and usually a short
vitrification range and sometimes a high
firing shrinkage.
Paints
In this industry, foliated, fibrous or
lamellar talc of fine mesh (300 mesh) is
preferred. It is used as a paint or an
extender in paint industry. Colour,
particle size and oil absorption are the
main criteria for selecting talc for
paint manufacture. Talc suitability for
paint should have volatile matter below
0.75%, oil absorption within 5 of the
approved sample and solubility not more
than 0.25% in water. Asbestine is the
trade name given to fibrous talc
suitable for paint making.
Other uses
A fair proportion of medium to inferior
grades of talc is used in the
manufacture of perticides and
insecticides. Talc is used here as a
carrier. Talc powder prevents
infestation of food grains from
insectsand pests and hence it is
sprinkled over food grains kept in big
godowns. Other uses are for making
crayons for marking purposes and for tailors' chalk
Recommended Filled of Application
| Kind of powder |
Talc |
Mica |
Kaolin |
Red Iron oxide |
Fluorine |
Dolomite |
Calcite |
Bentonite |
Barite |
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