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Physical, chemical and biological, London

London gravestone Visit any graveyard - but please respect it - and you will always see a variety of weathering processes in action. You can see how rock types used for different gravestones weather at different rates - you can tell from the dates on them!

In the example below, a gravestone made of thinly-bedded sandstone (the type often used as paving slabs in older towns and cities) has been damaged badly. Water seeped downwards between the vertically-oriented layers at the top of the stone, froze and expanded, eventually causing the layers to split and break off. This is physical weathering by freeze-thaw action.

Meanwhile, chemical weathering is helping to break down the cementing material between the sandstone grains, aided by biological weathering (from acids released by algae and lichen on the surface), so the rock surface is gradually crumbling away.
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