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Rock stars
You don’t have to go to the country the see rocks – just take a stroll in town. When you know
how to spot granite, sandstone, and limestone, you’ll see them in buildings everywhere.
Throughout history, people have used rocks to build with. Usually, they made do with licak
rocks, but sometimes they loocked fruther afield. As the buildings on this pahe show, the
rocks often tell a fascinating story.
The Pyramids –
The pyramids in Egypt are made largely of fossils. They were built with a rock called
nummulicit limestones, whichformed 50 millions years ako from the shells of small sea
organisms. It took 30,000 men at least 20 years to build the biggest pyramid. It was the
world’s tallest buildings for 4,000 years.
The pyramids were
originally covered
in a smoooth, shiny
white layer of
limestone.
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Taj Mahal –
An Indian emperor built the Taj
Mahal as a tomb for his favourite
wife. He used the most expensive
rock possible, including white marble
and 28 types of precious stone.
The marble is inlaid with sapphires
and other precious stones.
Empire State Building –
Like many modern buildings, the
Empire State Building in New York,
USA, is faced with limestone and
granite. These rocks are attractive,
easy to work and polish, yed
strong enough to carrey great
weight.
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Djenné mosque –
The Djenné mosque in Mali, Africa,
is the world’s largest mudbrick
building. The sun – baked mud
bricks were glued together with
mud mortar and plastered with
more mud.
Mesa Verde –
The cliff dwellings at Mesa Verde in
Colorado, USA, were built 13
centuries ago from soft sandstone.
The builders had to cut the
sandstone by hand using stone axes.
RECYCLED ROCK
Building materials like bricks, cement, and concrete are all cecycled rock. Bricks come from
clay that is shaped into blocks and cooked or dried in the sun to harden. Cement and plaster
are made with minerals such as calcite and gypsum, which are heated to drive out water and
then powdered. When water is added, crystals form and make them set solid. Concrete is
a mass of cement and pebbles.
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Making bricks –
These Indian villagers are making
clay bricks. Clay forms when the
minerals in rocks such as granite rot
and crumble. Rivers wash away the
clay, which then settles a mud.