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4.
THE USE OF ROCKS
The evolution of humans since the Palaeolithic Age has been linked to the use
of rocks for building, ornamentation or making utensils for hunting. Today, we
continue to use rocks for these activities.
The main uses of rocks are building, ornamentation and as a source of fuels and
technological materials.
❚
Building materials
: some rocks are used directly. Others are modified for
building purposes.
Cement, concrete, ceramics and glass are some of the most commonly used
building materials. They all come from rocks.
Key concepts
❚
Rocks are used, directly
or modified, as building
materials.
❚
Rocks also have ornamental
uses, as fossil fuels or as
a source of minerals for
technological use.
Cement
is obtained by grinding and
heating limestone and clay. It is mixed
with water to create a substance that
hardens
3
when dry. It allows us to stick
rocks together.
Concrete
is created by mixing cement,
water, sand and gravel. When dry, it
is harder and stronger than cement.
This is why it is used for pillars and
foundations.
Ceramics
are made with pulverised
clay mixed with water, modelled and
cooked at high temperatures.
They are used to make bricks, tiles
or dishes.
Glass
is created from quartz present
in sand. Sand is placed in an oven at a
high temperature and it melts. When
cooled, glass can be shaped in different
ways.
3
harden
:
to become hard
❚
Ornamental rocks
: marble, granite, slate and basalt are often used in decoration.
Due to their beauty once they have been carved and polished, these rocks are
used in sculptures, floors of buildings and many other decorative elements in the
interior and exterior of buildings.
❚
Source of fossil fuels
: sedimentary rocks such as coal and oil are used because
they produce a lot of energy when burnt.
❚
Source of minerals for technological use
: rocks rich in quartz are a source of
silicon, which is used to make computer processors or photovoltaic solar panels.
Aluminium, obtained from a sedimentary rock called bauxite, is used to make
many objects such as planes, soft drink cans or kitchen utensils.
Remember
28.
Make a table of rocks
used to make building
materials. Include what
materials they are used
to make and the uses of
those materials.
29.
Which types of rocks
are usually used for
decoration?
Understand
30.
Explain the difference
between concrete and
cement.
