Nothing is permanent
Can a Rock Turn Into a Different Rock?
Rocks are constantly recycled: heat, pressure and weathering turn each kind into the others.
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Step 1 of 5
There are three broad kinds of rock.
Rock formed from cooled melt, rock formed from compressed layers of grains, and rock changed by heat and pressure without melting.
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Step 2 of 5
Molten rock cools into solid rock.
Magma rising from below cools and crystallises, quickly at the surface into fine glassy rock or slowly at depth into coarse crystals.
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Step 3 of 5
Weather breaks it down into grains.
Exposed rock is attacked by frost, rain and roots, reduced to fragments and carried away by rivers to settle somewhere else.
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Step 4 of 5
Buried layers get squeezed into new rock.
Grains pile up, are buried under more layers, and the weight plus mineral cement presses them into solid stone once again.
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Step 5 of 5
Heat and pressure can change it again.
Buried deeper or caught in a mountain-building collision, rock is cooked and squeezed into a new form without ever melting. The cycle has run so long that the oldest surviving crust is about four billion years old.
Some rock at the base of ancient mountain ranges has been round the cycle several times over billions of years.
The short version
Weather grinds rock to grains, burial and mineral cement press the grains back into stone, and deeper heat cooks stone into a new form without ever melting it. The oldest surviving crust is four billion years old.
Try it yourself
Look at a pebble beach. The variety of colours and textures represents rocks at very different points in this cycle.