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An introduction to geology
An introduction to geology

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1.3 Rock textures

Due to how the three sorts of rock are formed, they appear quite different when you look at them closely. All rocks are formed of smaller parts, called ‘grains’.

Described image
Figure 1.4 From left to right, igneous, metamorphic and sedimentary rocks

As igneous rocks begin to cool down from the molten state, the grains are crystals which grow together to form an interlocking texture, with the crystals touching each other.

The grains in metamorphic rocks are made up of crystals too, but because they are usually formed under pressure, the crystals are often aligned in one direction and form bands of different colours or shapes of crystal.

As sedimentary rocks are formed of bits of other things stuck together, they look just like that, with individual grains (called ‘clasts’ in sedimentary rocks) cemented together.