Contact metamorphism

When magma comes into contact with a sedimentary rock, its heat makes the rock much harder. Quartz grains in sandstone recrystallise to form quartzite. Limestone made of shell fragments may form a coarse-grained marble. Mudstone changes into dark, fine-grained hornfels.

As well as heating the surrounding rocks, magma can add elements such as fluorine and boron to them. These new ingredients take part in the changes to the rocks caused by heating. If the rocks are layered, each layer will contain a different set of minerals.

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Changing Rocks and MineralsRegional metamorphismGarnetsGems in Marble