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In commerce, vermiculite which expands more than 10 times the
original volume is regarded of good quality. With an expansion below
10 times the original volume, vermiculite is considered of low grade.
It is believed that the mineral, now known as vermiculite, was
originally observed in Worcester, Massachusetts, in 1824. When exposed
to a flame, the mineral would expand into a variety of fanciful forms
resembling small worms. Because of this peculiar property, Thomas H.
Webb gave it the name vermiculite, or worm breeder.
The Present Scenario
Vermiculite plaster is widely used for better acoustics and reduction
of noise in auditoriums, wireless studios, theatres, hospitals etc.
Vermiculite mixed with three parts of gypsum is used as plaster for
is the name used in commerce for a group of micaceous minerals that
expand or exfoliate many times (commercial varieties esfoliate 8 to 20
times or more) the original thickness when heated. They show the
characteristic micaceous structure of basal cleavage and occur as
soft, pliable inelastic laminae. Their basal cleavages are not so
perfect as those of mica. Vermiculite exists in a wide range of
colours from black through various shades of brown to yellow. Its
chemical composition varies widely consisting of a complex hydrated
aluminium, magnesium silicate and hence the analysis of the mineral is
of little use in determining the vermiculite for commercial utility; a
technical trial of the material provides the only satisfactory test.
Vermiculite owes its commercial utility to its property of exfoliation
when heated. It exfoliates into a yellow to bronze coloured mass
giving an appearance of a cluster of worms - vermiculus, an Italian
word for worm from which it has derived its name as vermiculite. Some
authorities quote the Latin word vermiculari from which the name
vermicultie might have been derived.
- Copper Vermiculite
- Eastonite (of Hamilton)
- Lucasite (of Chatard)
Alumina,10-17% Iron oxides,5-22% Magnesium oxide,11-13%
Gray white Yellow brown
|Vitreous - Dull
Vermiculite crystallizes in the monoclinic system, and the crystal
faces are often marked wth triangular lines at 60 degrees and 120
degrees. X-ray studies have indicated that vermiculite constitutes a
specific type with a definite structure differing from that of mica or
chlorite. From the tabulation of a number of analyses, Gruner has
stated that its average composition can be represented by the formula
whereas J. B. Myers gives the structural formula as (OH)2
(Si, Al, Fe)4
The indefinite and variable chemical composition of vermiculite is
indicated by the following ranges of major constituents in
water content (free water and water of crystallization)
varieties of vermiculite have been identified and listed. Colloquilly
(mostly in England) vermiculite is known as Sunshine, Feather Gold and
Golden mica. In Japan, it is known as Leach stone.
Its hardness reanges from 1.5 to 3. The specific gravity of the crude
material as mined is about 2.5, fusion point is approximately 1335ºC
and specific heat is 0.2. The property of exfoliation together with
the development of golden, bronzy or silvery lustre on heating is the
outstanding characteristic ofvermiculite. This is one of the most
important characteristics by which vermiculite differs from mica.
Exfoliation commences from varying temperatures with different
samples, in some cases as low as 150ºC. In industrial practice a
temperature range between 800ºC-1100ºC (for a period of 4
seconds to 2 minutes) is employed. The exfoliation takes place solely
in a direction perpendicular to the cleavage. Exfoliation is said to
result from the expulsion of combined water by the purely mechanical
effect of the sudden formations of steam. Certain qualities of
vermiculite exfoliate and develop lustre when immersed in cold
hydrogen peroxide (H2
) or other oxidising
agents such as a mixture of potassium permanganate (K2
and hydrochloric acid (HCl). In these cases the exfoliation is
probably caused by the mechanical force involved in the liberation of
oxygen from the reagent by the catalyst present in the vermiculite. It
has been suggested that exchangeable magnesium ions present in the
water layers are responsible for the liberation of oxygen. The
moisture content of the mineral has a bearing on its price, and the
combined water content gives an indication of exfoliation properties.
Vermiculite is always used in exfoliated form. When exfoliated it
possesses nearly 10 to 11 times less bulk density than the original
volume. In commerce, vermiculite which expands more than 10 times the
original volume. In commerce, vermiculite which expands more than 10
times the original volume is regarded of good quality. With an
expansion below 10 times the original volume, vermiculite is
considered of low grade. The low bulk density, comparative high
refractoriness, low thermal conductivity and chemical inertness make
vermiculite satisfactory for many types of thermal and acoustic
insulations. One of its large commercial uses is as an aggregate in
light weight concrete and hard wall-plaster because of its acoustic
and thermal insulating and fire-resisting qualities. The density of
raw vermiculite is 50 to 90 lbs. per cu. ft. While that of the
exfoliated one is 5-10 lbs. per cu. ft. It is therefore extensively
used in concrete work to save weight. Vermiculite concrete weighs
20-25 per cu. ft. as against and concrete which weighs about 100 lbs.
per cu. ft. Vermiculite concrete has the same advantages as concrete
made with pumice and perlite. Refractory insulations both in the form
of loose vermiculite fill and vermiculite bricks are used in furnaces
and kilns up to 1100ºC. About 60% of the present world
consumptions is in the form of loose fill when the expanded material
is merely pured like dry sand into wall spaces or applied over ceiling
constructions or attics of residential buildings with a view to
insulating homes against cold in winter and heat in summer. One inch
of Unifil, a trade name of a particular expanded vermiculite, holds
back as much of 2½ ft. brick wall or wall of concrete 3¾ ft.
thick. As a light-weight aggregate it is extensively used in
prefabricated houses. Vermiculite concrete in the form of monolithic
cast is used in sound-absorbing panels in aeroplane engine testing
Vermiculite, being a granular expanded aggregate with numerous air
voids, when mixed with a suitable binder develops sound insulating
properties. Vermiculite plaster is widely used for better acoustics
and reduction of noise in auditoriums, wireless studios, theatres,
hospitals etc. Vermiculite mixed with three parts of gypsum is used as
plaster for sound-absorbing purposes. A new building material called
Pyrok, consisting of vermiculite bonded with lime and cement is
marketed in England.
More than hundred major and minor uses of vermiculite have been
developed in the fields of agriculture, pesticides, lubricants,
disinfectants, plastics and light-weight insulating bricks.
A canadian steel company ships red hot steel ingots for a distance of
288 km from open hearth to mill plant, embedded in loose vermiculite.
A temperature loss of less than 9 per cent is reported. The
vermiculite is reused.
Unexfoliated vermiculate has a few minor uses, such as for
circulation in drilling mud and in the annealing of steel. When
unexfoliated vermiculate is reacted with concentrated H2
it produces a pure form of silica in flake form. This product is known
as 'samisilite'. It is used as adehydrating medium in air conditioning
plants since it can absorb about 20 per cent its weight of water. The
potency of this product may be revived by heating.
There are three important mining centres of vermiculite in the world.
in the Transvaal, Rep. of South Africa
transvaal deposit is by far the best known in the world and it
supplies all European countries. USA also imports considerable
quantities from Transvaal for its better quality and blending
qualities. oTher countries reporting negligible to small production
are Kenya, Tanzania and Malawi in Africa, Queensland, South Australia,
Western Australia, Argentina, Brazil, Egypt and Japan.
Vermiculite is mined at Phalaboreva in Palabora district. It is the
largest mine of vermiculite in the world. The mineral occurs in the
serpentinised pyroxenite of complex nature. The mine is worked by the
Transvaal Ore Co. Ltd.
The mine is worked by the open pit benching method, the benches being
5 metres high and from 9-45 metres wide. 150,000 tonnes of rocks are
removed from the mine each month consisting of 60,000-70,000 tonnes of
ore with 40 to 45% vermiculite. The Transvaal Ore Co. Ltd., markets 5
grades of vermiculite. Raw vermiculite is prepared by crushing,
drying, screening and winnowing. The ore is dried in rotary coal-fired
driers at a temperature of 600ºF. The dried material is of
different sizes of which the +5/8 in. variety is reduced in hammer
mills, screened into various sizes and cleaned by winnowers which
concentrate, middlings and waste. Middlings, mainly small thick
'books' of vermiculite, are returned to the hammer mills to be
The deposit is situated in Lincoln county near Libby.
Vermiculite is associated with pyroxenite and biotite. The rock mass
grades nearly pure biotite and vermiculite. Vermiculite is found as a
lenticular vein 6 to 30 metres wide and 300 metres long. The hill
containing vermiculite is mined systematically by benches employing
power shovel. The mined rock is treated at the mine site employing
grizzly table and vibrating screens to free waste rock.
The vermiculite is mined in Piedmont in
western South Carolina. Vermiculite is found in an altered mass of
pyroxenite in the country rock of schists and gneisses. The upper
portion of altered pyroxenite is vermiculite and the lower portion of
altered pyroxenite is vermiculite and the lower portion is biotite.
Vermiculite veins persist upto a depth of 5 to 6 metres from the
surface when biotite is encountered.
In all vermiculite has been reported in 14 states of the
United States. Besides Montana and South Carolina, the other important
producing states are California, Colorado, Georgia, North
Carolina, Texas, Nevada
Vermiculite is mined in the Urals where it is found in association
with dunite and pyroxenite intrusions which are widely known as a
source of platinum.
The most important deposit is located at Stenley ville near Perth,
Ontario and it has been observed over an area nearly three-fifth of a
mile long and in many places one-sixth of a mile wide. Production of
vermiculite in Canada is small.
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