Igneous and metamorphic rocks

Sorry - no fossils here!

Igneous rocks form from molten rock, and rarely have fossils in them.

Metamorphic rocks have been put under great pressure, heated, squashed or stretched, and fossils do not usually survive these extreme conditions. Generally it is only sedimentary rocks that contain fossils.

Granular polished black and white rock surface

Augen gneiss, a metamorphic rock with white feldspars ‘eyes’, black biotite mica and colourless quartz.

Do you know what these rocks are?

This is a metamorphic rock called gneiss. Gneiss often forms from the igneous rock granite.

This sample is banded (striped) and faulted - you can see a break running diagonally through the rock, where the stripes don't line up with each other. This fault shows us that the rock has been been put under a lot of pressure.

This is an igneous rock called basalt. Basalt is a dark rock formed from the lava that erupts from some types of volcano.

This sample looks a bit like Swiss cheese - it has a lot of holes in it. Molten rock often contains dissolved gases - these gases bubble out of the lava when it is still a liquid, but as the lava solidifies, the gas becomes trapped. It is this gas that forms the bubbles you see here.

This is an igneous rock called gabbro. Gabbro forms when a molten rock cools and crystallises.

It takes a long time for large amounts of molten rock to cool, so the crystals that form in gabbro are quite big. Granite also forms in this way, and has large crystals - so how do you tell gabbro and granite apart?

Gabbro and granite are made up of different types of minerals - generally gabbro is darker in colour than granite.

Igneous and metamorphic rocks

Do you know what these rocks are?

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