We may think that recycling is a modern feature of our world but, in fact, rocks have been recycled since the dawn of time. A single piece of rock, during Earths 4600 million- year existence, may have moved as lava from below the earths crust to the top of a mountain, been twisted and altered by pressure, eroded to the sea, and, by a process called subduction, transported back into the mantle which is semi-fluid.
The same piece of rock may have travelled around the globe, through the poles and the equator several times in its existence.

Most rocks are very old but some are new and forming as you read this article. They come in all the colours you can imagine and vary in hardness and texture. Their uses are in everything we see, Cement is made from Limestone and Mudrock, baked and powdered, British bricks are made from Jurassic clays from the age of the dinosaurs, Roofing is made from either natural slates or tiles made of clay. Tiles, washbasins and your loo are made out of clay from ancient rivers that ran through Dorset and Devon about 30 million years ago, Plaster is made from Gypsum, formed in a dried up lake bed around 250 million years ago. Concrete is cement mixed with aggregate, possibly deposited by an ice age and glass is made of pure sand mixed with limestone and salt.

The recycling of the rock creates three main types of rock:

1. Igneous rock, solidified from hot molten rock. These include Basalt, volcanic lava formed by melting in the Earth’s interior. Granite, molten rock that doesn’t reach the surface of the volcano and Pumice, lava with gas bubbles.
2. Metamorphic rock, a rock altered by heat and pressure inside the Earths crust. These include Slate, formed from layers of fine mud accumulated on the ocean floor, Schist and Gneiss, squashed and heated forms of slate, Serpentine, from Basalt and Marble, squashed and heated limestone.
3. Sedimentary rocks. Sandstones formed from sand grains eroded from older rocks. Limestones, made from fragments of sea creatures and Mudrock, simply mud hardened into rock. Chalk, a rock which dominates the south of England, was laid down in the Cretaceous period 65-100 million years ago when the sea levels were very much higher than they are today. Chalk is formed from millions of tiny algae which were eaten by shrimps ,then passed through as faecal pellets and piled up and compacted. So the chalk of the White cliffs of Dover is really just a huge pile of you know what.