Granite Basalt Sandstone Slate Limestone Marble Mica Chalk

Rock has always been the preferred building material of the ancient nobility and the priesthood. As long as you had plenty of cheap labour, a good supply of rock and a fair deal of mathematical and engineering expertise, building with stone was the only way to make sure your monument outlasted your own mortality.

All the great ancient buildings are made of stone. The Egyptian Pyramids were made with sedimentary limestone, igneous granite and maybe even capped with gold. Stonehenge was constructed with hard igneous basalt and sedimentary sarsen sandstone. The Taj Mahal in India is made of brilliant white metamorphic marble and the Moi statues of Easter Island from igneous volcanic tuff rock.

Some have withstood the ravages of time much better than others, but all were built to last with strength, beauty and grandeur.

This topic investigates the properties and uses of the more common rocks used for building: granite, basalt, sandstone, slate, limestone, marble, mica and chalk.

Granite
Granite is a beautiful and hard igneous rock capable of being cut and polished to a high mirror finish. It is usually used for facing or finishing off rather than as a construction stone. Granite is traditionally the stone chosen by both architects and engineers when permanence, enduring colour and texture, as well as freedom from deterioration and maintenance are the prime requirements. Many modern city buildings use granite for its beauty and ability to withstand chemical attack from pollution. Granite is also found in kitchens, where it is used for chopping blocks and bench tops because of its durability and chemical resistance.

Basalt
Basalt rock is very plentiful, making up most of the igneous rock on or near the surface of the Earth. In Victoria, basalt is sometimes referred to as 'Bluestone'. It is very hard and resists moisture and chemical attack. Used mainly in foundations or as road base, basalt was used in the construction of the inner circle of Stonehenge over 5 000 years ago in the U.K. and some of the more substantial buildings of the 19^th century England and Australia. Many of Melbourne's major churches, cathedrals and older schools have been built with basalt.

Sandstone
Also at Stonehenge, is a stone arrangement consisting of a horseshoe of tall uprights of sarsen sandstone encircled by a ring of tall sarsen uprights, all originally capped by horizontal sarsen lintels. The very large sandstone rocks were selected for their ability to be carved and shaped as well as for their durability. Many houses use sandstone in paving and wall construction, because it is easy to cut and prepare. Over long periods of time sandstone will wear, especially in steps and paving, but it is relatively cheap to replace.

Sandstone, being a sedimentary rock, is typically much softer than igneous rock, making it easier to work with and to cut precisely. Sandstone's colour is determined by its composition. Iron oxides create red sandstone, and other minerals produce white, yellow, or grey sandstone.

Slate
Slate is a hard metamorphic rock that is easily split into layers and cut. Used mainly in roofing of older houses, inside flooring and the bases of pool tables, slate is used for its durability. Usually dark grey, slate can vary in shade and colour.

Limestone
Limestone is a white sedimentary rock formed from particles of shells and bone from marine animals. The blocks of the Great Pyramid of Cheops in Giza, Egypt are made of limestone. High quality limestone can be cut and polished appearing like marble from a distance. The surface of the Cheops pyramid was once covered in polished limestone, much of which was removed to build the mosques and buildings of old Cairo.

Limestone is relatively easy to work with, but suffers badly from corrosion and chemical weathering. In the present dry climate of Egypt, this is less of a problem, although some degradation has occurred in the pyramids due to rising acidic ground water. In the polluted cities with acid rain, the calcium carbonate in the limestone reacts with the acid in the rain and soon dissolves the rock away.

Marble
Marble is the metamorphic rock formed from limestone. Usually a brilliant white, marble is prized for its ability to retain a high polish and its workability. Michelangelo's David is carved from a block of marble as are many Greek and Roman statues. Marble has traditionally been used for high quality finishes, flooring and staircases in the grandest buildings.

Hard-wearing and easily worked, marble's only downfall is its origin. Like limestone, marble is composed of calcium carbonate, so it is also badly affected by modern city pollution and acid rain.

Mica
Mica is a delicately layered metamorphic mineral which is slightly transparent. Because mica is highly heat resistant, in the past mica has been used in furnaces and fire place windows where normal glass would melt. Mica speckle is also used in paving, giving the glitter that makes steps and paths stand out as well as in nail polish glitter, make-up and lip sticks.

Chalk
Chalk, as used in schools, is a very soft sedimentary rock formed from seashells. Like limestone and marble, it is composed of calcium carbonate.

Summary
From the grandest and the oldest structures to everyday use, rocks have been and will always be an important building material.

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