Fossils on Friday – Metamorphic Rocks

Hello and welcome back to Fossils on Friday. Although today, we are taking another trip away from fossils and into the world of metamorphic rock! So what is metamorphic rock?

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Metamorphic rocks can often look like sedimentary rocks, but they have some key differences

Have you heard of the term ‘metamorphosis’ before? It’s the process by which animals appear to change from one form to another during their lifecycle. For instance, when a tadpole turns into a frog, or a caterpillar turns into a butterfly. Although it’s the same creature, same species, it has completely changed form – from a small wiggly thing to a hopping frog or a beautiful and delicate butterfly.

Metamorphosis is the term used to describe the change from a tadpole to a frog.

Metamorphosis and metamorphic come from the same root word in Greek, simply meaning to ‘change form or structure’. Just like the frog turns from a black squirmy tadpole to a green hopping frog, metamorphic rocks have also changed structure during their history.

Metamorphic rocks started out as either sedimentary or igneous rock. They were then exposed to heat, pressure, or both, which changes the chemical and molecular structure of the rock. This can melt it, make it brittle, harden, soften and many other different changes to the physical appearance. For instance, limestone, the same stuff that chalk belongs to, can be metamorphosed into marble, the hard shiny stone that Greek and Roman statues were made from!

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Limestone, such as the chalk in the White Cliffs of Dover can be metamorphosed into marble.

Metamorphic rocks are fascinating, and there are several examples throughout the UK. So join us over the next few weeks as we explore the world metamorphic rocks in Britain!