What is Pumice?
Pumice
is an extrusive type of volcanic
rock usually found in areas
where volcanoes are active or
has been active in the past.
Pumice is formed or produced
when lava with a very high
content of water and gases
(together these are called
volatiles) is thrown out (or
extruded) from an active
volcano. As the gas bubbles
escape from the lava, these
volatile material becomes
frothy. When this lava cools and
hardens, the result is a very
light rock material filled with
tiny bubbles of gas. It is very
lightweight and pumice is the
only rock that floats on water,
although it will eventually
become waterlogged and sink. It
is usually light-colored
(although there are red scoria
volcanic cinder pumice also),
indicating that it is a volcanic
rock high in silica content and
low in iron and magnesium, a
type usually classed as
rhyolite. If the lava
hardens quickly with few
volatiles, the resulting rock is
volcanic glass, or obsidian.
Pumice and obsidian are often
found together. We have
mountains of these red and grey
colored Pumice stones in the
Philippines.
In
commerce, pumice is the
term applied to larger pumice
stones, while pumicite
consists of fine grains or ash.
Pozzolan is a
fine-grained pumicious material
(both natural and man-made),
which combines with lime to make
a smooth, plaster-like cement.
These three similar materials
may be found and mined together,
but they have different
characteristics and different
uses.
Why is it called pumice?.
The
name pumice is taken from the
Latin word pumex, meaning
foam. Pozzolan (or pozzolana)
is an Italian word, named from
Pozzuoli, the place near Naples
where pozzolan was first mined
and used as cement, during Roman
times.
Which
countries has pumice?
Since
pumice is a volcanic rock, and
retains its useful properties
only when it is young and
unaltered, pumice deposits are
found in areas with young
volcanic fields. Worldwide, over
50 countries produce pumice
products. The largest producer
is Italy, which dominates
pozzolan production and also
produces some pumice. Other
major pumice producers are
Greece, Chile, Spain, Turkey,
and the United States.
In the
United States, Arizona,
California, New Mexico and
Oregon are the major producers
of pumice, accounting for the
majority of the nation’s pumice
and pumicite production.
What
are the uses of pumice?
Pumice
and pumicite are used to make
lightweight construction
materials such as concrete block
and concrete. About
three-quarters of pumice and
pumicite is consumed annually
for this purpose.
The
remainder of the pumice mined is
used in abrasives, horticulture,
landscaping, and for washing
blue jeans.
Pozzolan is used to make
fine-grained, lightweight cement
for finishing floors and
building interiors.
What
are the substitutes and
Alternative Sources of pumice?
Expandable shale can be
substituted for pumice and
pumicite in the building block
and concrete applications. There
is no lack of pumice and
pumicite, as world resources are
extensive. However, the costs
related to mining and trucking
the material from the mine to
processing plants and the market
will determine whether pumice
from a particular mine is cheap
enough to use. In other words,
it is economics, not the
abundance of pumice, which
determines whether or not
substitutes for pumice are
necessary.
