How people use different rocks
Chemistry · Key Stage 2 · The School
A rock is chosen for a reason
People have used rock for building for thousands of years. They do not pick a rock at random. They pick one whose properties suit the job — how hard it is, how it splits, and whether it soaks up water.
Granite, slate and limestone
GRANITE is very hard and does not wear away fast, so it is used for kerbstones and monuments. SLATE splits into thin, flat, waterproof sheets, so it is used for roof tiles. LIMESTONE is soft enough to cut easily but strong enough to build with, so it is used for walls and steps.
Chalk and sandstone too
CHALK is very soft and a little crumbly. It is used to make cement and, ground up, toothpaste. SANDSTONE is easy to cut into blocks when first quarried but hardens over time, so many old buildings and bridges are built from it.
Suppose a shed roof leaks and you must pick a rock to mend it. Four rocks are on the table: chalk, sandstone, granite and slate. Step 1: say what a roof needs. Roof tiles are flat pieces that overlap to keep rain out. So the rock must come in flat pieces and must not let water through. Step 2: test for water. Chalk soaks water up, and most sandstone does too, so cross them out. Granite and slate take in almost none, so they stay. Four rocks are now two. Step 3: check the shape. Granite is made of interlocking crystals, with no layers inside it. Slate splits easily into thin, flat sheets, which is just what tiles need. Four rocks are now one: slate. The same steps work for a kitchen worktop. It needs a rock harder than the tools used on it, so granite suits it. The Natural Stone Institute says granite usually copes with heat up to about 250 degrees Celsius, but strong heat on one spot can crack it. Next time you see a stone building, ask what job its rock is doing.